Fix failing psasim tests

This commit fixes failing psasim tests by ensuring that
MBEDTLS_VERSION_C is defined before attempting to access version
information.

Signed-off-by: Harry Ramsey <harry.ramsey@arm.com>
diff --git a/tests/psa-client-server/psasim/src/server.c b/tests/psa-client-server/psasim/src/server.c
index 10ab5a2..44939f1 100644
--- a/tests/psa-client-server/psasim/src/server.c
+++ b/tests/psa-client-server/psasim/src/server.c
@@ -52,12 +52,14 @@
     psa_msg_t msg = { -1 };
     const int magic_num = 66;
     int client_disconnected = 0;
-    char mbedtls_version[18];
     extern psa_status_t psa_crypto_call(psa_msg_t msg);
     extern psa_status_t psa_crypto_close(void);
 
+#if defined(MBEDTLS_VERSION_C)
+    char mbedtls_version[18];
     mbedtls_version_get_string_full(mbedtls_version);
     SERVER_PRINT("%s", mbedtls_version);
+#endif
 
     parse_input_args(argc, argv);
     SERVER_PRINT("Starting");