tegra: 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>

arch/arm/mach-tegra/dt-setup.c

@@ -3,6 +3,7 @@
  * Copyright (c) 2010-2016, NVIDIA CORPORATION.
  */
 
+#include <env.h>
 #include <fdtdec.h>
 #include <stdlib.h>
 #include <asm/arch-tegra/cboot.h>