Include configuration file to headers

Add inclusion to configration file in header files,
instead of relying on other header files to include
the configuration file. This issue resolves #1371

include/mbedtls/ecp.h

@@ -36,6 +36,12 @@
 #ifndef MBEDTLS_ECP_H
 #define MBEDTLS_ECP_H
 
+#if !defined(MBEDTLS_CONFIG_FILE)
+#include "config.h"
+#else
+#include MBEDTLS_CONFIG_FILE
+#endif
+
 #include "bignum.h"
 
 /*