mbedtls: Add a shim header to account for including "mbedtls/config.h" directly in program

Previously this resulted in a config mismatch between default config and esp_config.h

Closes https://github.com/espressif/esp-idf/issues/711

components/mbedtls/port/include/mbedtls/config.h

@@ -0,0 +1,9 @@
+/* This shim header is added so that any application code
+   which includes "mbedtls/config.h" directly gets the correct
+   config. */
+#pragma once
+#if !defined(MBEDTLS_CONFIG_FILE)
+#include_next "mbedtls/config.h"
+#else
+#include MBEDTLS_CONFIG_FILE
+#endif