congatec: Include env.h to permit reading the environment

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

Signed-off-by: Simon Glass <sjg@chromium.org>
Signed-off-by: Tom Rini <trini@konsulko.com>

board/congatec/cgtqmx8/cgtqmx8.c

@@ -4,6 +4,7 @@
  * 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>