Fix issue with reuse of custom yotta configs for target_config.h (#530)

diff --git a/include/mbedtls/config.h b/include/mbedtls/config.h
index 3b7c85b..8e263b0 100644
--- a/include/mbedtls/config.h
+++ b/include/mbedtls/config.h
@@ -2567,7 +2567,11 @@
 /* \} name SECTION: Customisation configuration options */
 
 /* Target and application specific configurations */
-//#define YOTTA_CFG_MBEDTLS_USER_CONFIG_FILE "target_config.h"
+//#define YOTTA_CFG_MBEDTLS_TARGET_CONFIG_FILE "mbedtls/target_config.h"
+
+#if defined(TARGET_LIKE_MBED) && defined(YOTTA_CFG_MBEDTLS_TARGET_CONFIG_FILE)
+#include YOTTA_CFG_MBEDTLS_TARGET_CONFIG_FILE
+#endif
 
 /*
  * Allow user to override any previous default.