Update guards for crypto only builds

This commit updates the guards for crypto only builds to prevent error.c
being built.

Signed-off-by: Harry Ramsey <harry.ramsey@arm.com>
diff --git a/scripts/config.py b/scripts/config.py
index beeb5e2..0641a23 100755
--- a/scripts/config.py
+++ b/scripts/config.py
@@ -218,6 +218,8 @@
             'MBEDTLS_DEBUG_C', # part of libmbedtls
             'MBEDTLS_NET_C', # part of libmbedtls
             'MBEDTLS_PKCS7_C', # part of libmbedx509
+            'MBEDTLS_ERROR_C', # part of libmbedx509
+            'MBEDTLS_ERROR_STRERROR_DUMMY', # part of libmbedx509
     ]:
         return False
     if name in EXCLUDE_FROM_CRYPTO: