Add OAEP placeholders in asymmetric encrypt/decrypt

Replace PSS placeholders by OAEP placeholders. PSS is a signature
algorithm, not an encryption algorithm.

Fix typo in PSA_ALG_IS_RSA_OAEP_MGF1.
diff --git a/library/psa_crypto.c b/library/psa_crypto.c
index 2a0d59c..cd20738 100755
--- a/library/psa_crypto.c
+++ b/library/psa_crypto.c
@@ -1458,7 +1458,7 @@
         else
 #endif /* MBEDTLS_PKCS1_V15 */
 #if defined(MBEDTLS_PKCS1_V21)
-        if( alg == PSA_ALG_RSA_PSS_MGF1 )
+        if( PSA_ALG_IS_RSA_OAEP_MGF1( alg ) )
         {
             return( PSA_ERROR_NOT_SUPPORTED );
         }
@@ -1535,7 +1535,7 @@
         else
 #endif /* MBEDTLS_PKCS1_V15 */
 #if defined(MBEDTLS_PKCS1_V21)
-        if( alg == PSA_ALG_RSA_PSS_MGF1 )
+        if( PSA_ALG_IS_RSA_OAEP_MGF1( alg ) )
         {
             return( PSA_ERROR_NOT_SUPPORTED );
         }