Include configuration file for all headers

Include the configuration file for all headers that were not
included.
diff --git a/include/mbedtls/pkcs5.h b/include/mbedtls/pkcs5.h
index d4bb36d..f201250 100644
--- a/include/mbedtls/pkcs5.h
+++ b/include/mbedtls/pkcs5.h
@@ -26,6 +26,12 @@
 #ifndef MBEDTLS_PKCS5_H
 #define MBEDTLS_PKCS5_H
 
+#if !defined(MBEDTLS_CONFIG_FILE)
+#include "config.h"
+#else
+#include MBEDTLS_CONFIG_FILE
+#endif
+
 #include "asn1.h"
 #include "md.h"