Include configuration file for all headers

Include the configuration file for all headers that were not
included, and for new headers introduced.
diff --git a/include/mbedtls/ecdh.h b/include/mbedtls/ecdh.h
index cbd4841..e70865c 100644
--- a/include/mbedtls/ecdh.h
+++ b/include/mbedtls/ecdh.h
@@ -34,6 +34,12 @@
 #ifndef MBEDTLS_ECDH_H
 #define MBEDTLS_ECDH_H
 
+#if !defined(MBEDTLS_CONFIG_FILE)
+#include "config.h"
+#else
+#include MBEDTLS_CONFIG_FILE
+#endif
+
 #include "ecp.h"
 
 /*