Remove output buffer limitation for PSA with GCM.

The requirement of minimum 15 bytes for output buffer in
psa_aead_finish() and psa_aead_verify() does not apply
to the built-in implementation of the GCM.

Alternative implementations are expected to verify the
length of the provided output buffers and to return
the MBEDTLS_ERR_GCM_BUFFER_TOO_SMALL in case the
buffer length is too small.

Signed-off-by: Mateusz Starzyk <mateusz.starzyk@mobica.com>

library/psa_crypto.c

@@ -201,6 +201,8 @@ psa_status_t mbedtls_to_psa_error( int ret )
 
         case MBEDTLS_ERR_GCM_AUTH_FAILED:
             return( PSA_ERROR_INVALID_SIGNATURE );
+        case MBEDTLS_ERR_GCM_BUFFER_TOO_SMALL:
+            return( PSA_ERROR_BUFFER_TOO_SMALL );
         case MBEDTLS_ERR_GCM_BAD_INPUT:
             return( PSA_ERROR_INVALID_ARGUMENT );