Fix and simplify *-PSK ifdef's
diff --git a/library/ssl_cli.c b/library/ssl_cli.c
index 4da7149..6e981e0 100644
--- a/library/ssl_cli.c
+++ b/library/ssl_cli.c
@@ -1147,9 +1147,7 @@
           POLARSSL_KEY_EXCHANGE_ECDHE_ECDSA_ENABLED ||
           POLARSSL_KEY_EXCHANGE_ECDHE_PSK_ENABLED */
 
-#if defined(POLARSSL_KEY_EXCHANGE_PSK_ENABLED) ||                           \
-    defined(POLARSSL_KEY_EXCHANGE_DHE_PSK_ENABLED) ||                       \
-    defined(POLARSSL_KEY_EXCHANGE_ECDHE_PSK_ENABLED)
+#if defined(POLARSSL_KEY_EXCHANGE__SOME__PSK_ENABLED)
 static int ssl_parse_server_psk_hint( ssl_context *ssl,
                                       unsigned char **p,
                                       unsigned char *end )
@@ -1179,9 +1177,7 @@
 
     return( ret );
 }
-#endif /* POLARSSL_KEY_EXCHANGE_PSK_ENABLED ||
-          POLARSSL_KEY_EXCHANGE_DHE_PSK_ENABLED
-          POLARSSL_KEY_EXCHANGE_ECDHE_PSK_ENABLED */
+#endif /* POLARSSL_KEY_EXCHANGE__SOME__PSK_ENABLED */
 
 #if defined(POLARSSL_KEY_EXCHANGE_RSA_ENABLED) ||                           \
     defined(POLARSSL_KEY_EXCHANGE_RSA_PSK_ENABLED)
@@ -1872,10 +1868,7 @@
     else
 #endif /* POLARSSL_KEY_EXCHANGE_ECDHE_RSA_ENABLED ||
           POLARSSL_KEY_EXCHANGE_ECDHE_ECDSA_ENABLED */
-#if defined(POLARSSL_KEY_EXCHANGE_PSK_ENABLED) ||                           \
-    defined(POLARSSL_KEY_EXCHANGE_RSA_PSK_ENABLED) ||                       \
-    defined(POLARSSL_KEY_EXCHANGE_DHE_PSK_ENABLED) ||                       \
-    defined(POLARSSL_KEY_EXCHANGE_ECDHE_PSK_ENABLED)
+#if defined(POLARSSL_KEY_EXCHANGE__SOME__PSK_ENABLED)
     if( ciphersuite_info->key_exchange == POLARSSL_KEY_EXCHANGE_PSK ||
         ciphersuite_info->key_exchange == POLARSSL_KEY_EXCHANGE_RSA_PSK ||
         ciphersuite_info->key_exchange == POLARSSL_KEY_EXCHANGE_DHE_PSK ||
@@ -1964,10 +1957,7 @@
         }
     }
     else
-#endif /* POLARSSL_KEY_EXCHANGE_PSK_ENABLED ||
-          POLARSSL_KEY_EXCHANGE_RSA_PSK_ENABLED ||
-          POLARSSL_KEY_EXCHANGE_DHE_PSK_ENABLED ||
-          POLARSSL_KEY_EXCHANGE_ECDHE_PSK_ENABLED */
+#endif /* POLARSSL_KEY_EXCHANGE__SOME__PSK_ENABLED */
 #if defined(POLARSSL_KEY_EXCHANGE_RSA_ENABLED)
     if( ciphersuite_info->key_exchange == POLARSSL_KEY_EXCHANGE_RSA )
     {
diff --git a/library/ssl_srv.c b/library/ssl_srv.c
index 6db92d6..79c63fd 100644
--- a/library/ssl_srv.c
+++ b/library/ssl_srv.c
@@ -2353,9 +2353,7 @@
 }
 #endif /* POLARSSL_KEY_EXCHANGE_RSA_ENABLED */
 
-#if defined(POLARSSL_KEY_EXCHANGE_PSK_ENABLED) ||                           \
-    defined(POLARSSL_KEY_EXCHANGE_DHE_PSK_ENABLED) ||                       \
-    defined(POLARSSL_KEY_EXCHANGE_ECDHE_PSK_ENABLED)
+#if defined(POLARSSL_KEY_EXCHANGE__SOME__PSK_ENABLED)
 static int ssl_parse_client_psk_identity( ssl_context *ssl, unsigned char **p,
                                           const unsigned char *end )
 {
@@ -2421,9 +2419,7 @@
 
     return( ret );
 }
-#endif /* POLARSSL_KEY_EXCHANGE_PSK_ENABLED ||
-          POLARSSL_KEY_EXCHANGE_DHE_PSK_ENABLED ||
-          POLARSSL_KEY_EXCHANGE_ECDHE_PSK_ENABLED */
+#endif /* POLARSSL_KEY_EXCHANGE__SOME__PSK_ENABLED */
 
 static int ssl_parse_client_key_exchange( ssl_context *ssl )
 {
diff --git a/library/ssl_tls.c b/library/ssl_tls.c
index e254f3a..7450d34 100644
--- a/library/ssl_tls.c
+++ b/library/ssl_tls.c
@@ -825,10 +825,7 @@
 #endif /* POLARSSL_SHA512_C */
 #endif /* POLARSSL_SSL_PROTO_TLS1_2 */
 
-#if defined(POLARSSL_KEY_EXCHANGE_PSK_ENABLED) ||                           \
-    defined(POLARSSL_KEY_EXCHANGE_RSA_PSK_ENABLED) ||                       \
-    defined(POLARSSL_KEY_EXCHANGE_DHE_PSK_ENABLED) ||                       \
-    defined(POLARSSL_KEY_EXCHANGE_ECDHE_PSK_ENABLED)
+#if defined(POLARSSL_KEY_EXCHANGE__SOME__PSK_ENABLED)
 int ssl_psk_derive_premaster( ssl_context *ssl, key_exchange_type_t key_ex )
 {
     unsigned char *p = ssl->handshake->premaster;
@@ -926,10 +923,7 @@
 
     return( 0 );
 }
-#endif /* POLARSSL_KEY_EXCHANGE_PSK_ENABLED ||
-          POLARSSL_KEY_EXCHANGE_RSA_PSK_ENABLED ||
-          POLARSSL_KEY_EXCHANGE_DHE_PSK_ENABLED ||
-          POLARSSL_KEY_EXCHANGE_ECDHE_PSK_ENABLED */
+#endif /* POLARSSL_KEY_EXCHANGE__SOME__PSK_ENABLED */
 
 #if defined(POLARSSL_SSL_PROTO_SSL3)
 /*
@@ -3675,10 +3669,7 @@
 }
 #endif /* POLARSSL_X509_CRT_PARSE_C */
 
-#if defined(POLARSSL_KEY_EXCHANGE_PSK_ENABLED) ||                           \
-    defined(POLARSSL_KEY_EXCHANGE_RSA_PSK_ENABLED) ||                       \
-    defined(POLARSSL_KEY_EXCHANGE_DHE_PSK_ENABLED) ||                       \
-    defined(POLARSSL_KEY_EXCHANGE_ECDHE_PSK_ENABLED)
+#if defined(POLARSSL_KEY_EXCHANGE__SOME__PSK_ENABLED)
 int ssl_set_psk( ssl_context *ssl, const unsigned char *psk, size_t psk_len,
                  const unsigned char *psk_identity, size_t psk_identity_len )
 {
@@ -3714,10 +3705,7 @@
     ssl->f_psk = f_psk;
     ssl->p_psk = p_psk;
 }
-#endif /* POLARSSL_KEY_EXCHANGE_PSK_ENABLED ||
-          POLARSSL_KEY_EXCHANGE_RSA_PSK_ENABLED ||
-          POLARSSL_KEY_EXCHANGE_DHE_PSK_ENABLED ||
-          POLARSSL_KEY_EXCHANGE_ECDHE_PSK_ENABLED */
+#endif /* POLARSSL_KEY_EXCHANGE__SOME__PSK_ENABLED */
 
 #if defined(POLARSSL_DHM_C)
 int ssl_set_dh_param( ssl_context *ssl, const char *dhm_P, const char *dhm_G )
@@ -4385,9 +4373,7 @@
     }
 #endif
 
-#if defined(POLARSSL_KEY_EXCHANGE_PSK_ENABLED) ||                           \
-    defined(POLARSSL_KEY_EXCHANGE_DHE_PSK_ENABLED) ||                       \
-    defined(POLARSSL_KEY_EXCHANGE_ECDHE_PSK_ENABLED)
+#if defined(POLARSSL_KEY_EXCHANGE__SOME__PSK_ENABLED)
     if( ssl->psk != NULL )
     {
         memset( ssl->psk, 0, ssl->psk_len );