congatec: Include env.h to permit reading the environment

This file reads from the environment but does not include the correct
header. Update it.

Drop the unnecessary config.h while we are here.

Signed-off-by: Simon Glass <sjg@chromium.org>

board/congatec/cgtqmx8/cgtqmx8.c

@@ -3,7 +3,8 @@
  * Copyright 2018 congatec AG
  * Copyright (C) 2019 Oliver Graute <oliver.graute@kococonnector.com>
  */
-#include <config.h>
+
+#include <env.h>
 #include <errno.h>
 #include <linux/libfdt.h>
 #include <fsl_esdhc.h>