Implement PK Opaque RSA PSS signature

Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
diff --git a/library/pk_wrap.c b/library/pk_wrap.c
index a9c3c71..852c46e 100644
--- a/library/pk_wrap.c
+++ b/library/pk_wrap.c
@@ -1501,7 +1501,8 @@
 
 static int pk_opaque_rsa_can_do( mbedtls_pk_type_t type )
 {
-    return( type == MBEDTLS_PK_RSA );
+    return( type == MBEDTLS_PK_RSA ||
+            type == MBEDTLS_PK_RSASSA_PSS );
 }
 
 static int pk_opaque_sign_wrap( void *ctx, mbedtls_md_type_t md_alg,