Fix and simplify *-PSK ifdef's
diff --git a/programs/ssl/ssl_server2.c b/programs/ssl/ssl_server2.c
index 0148103..8e7ee0e 100644
--- a/programs/ssl/ssl_server2.c
+++ b/programs/ssl/ssl_server2.c
@@ -144,17 +144,13 @@
 #define USAGE_IO ""
 #endif /* POLARSSL_X509_CRT_PARSE_C */
 
-#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)
 #define USAGE_PSK                                                   \
     "    psk=%%s              default: \"\" (in hex, without 0x)\n" \
     "    psk_identity=%%s     default: \"Client_identity\"\n"
 #else
 #define USAGE_PSK ""
-#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_SSL_SESSION_TICKETS)
 #define USAGE_TICKETS                                       \
@@ -213,9 +209,7 @@
     int listen_fd;
     int client_fd = -1;
     unsigned char buf[1024];
-#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)
     unsigned char psk[256];
     size_t psk_len = 0;
 #endif
@@ -473,9 +467,7 @@
             opt.min_version = ciphersuite_info->min_minor_ver;
     }
 
-#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)
     /*
      * Unhexify the pre-shared key if any is given
      */
@@ -523,9 +515,7 @@
             psk[ j / 2 ] |= c;
         }
     }
-#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 */
 
     /*
      * 0. Initialize the RNG and the session data
@@ -739,9 +729,7 @@
         ssl_set_own_cert( &ssl, &srvcert2, &pkey2 );
 #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)
     ssl_set_psk( &ssl, psk, psk_len, (const unsigned char *) opt.psk_identity,
                  strlen( opt.psk_identity ) );
 #endif