Update symmetric only reference config to include config_psa.h

Since the symmetric only reference config is utilizing PSA
crypto library builds, the config file needs to included the
new config_psa.h so that all the PSA feature macros are setup
properly for the test.

Signed-off-by: John Durkop <john.durkop@fermatsoftware.com>
diff --git a/configs/config-symmetric-only.h b/configs/config-symmetric-only.h
index 054cb9e..f05a0d7 100644
--- a/configs/config-symmetric-only.h
+++ b/configs/config-symmetric-only.h
@@ -92,6 +92,8 @@
 #define MBEDTLS_VERSION_C
 #define MBEDTLS_XTEA_C
 
+#include "mbedtls/config_psa.h"
+
 #include "check_config.h"
 
 #endif /* MBEDTLS_CONFIG_H */