env: Move env_set() to env.h

Move env_set() over to the new header file.

Acked-by: Joe Hershberger <joe.hershberger@ni.com>
Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/board/udoo/neo/neo.c b/board/udoo/neo/neo.c
index d51f648..5c468a6 100644
--- a/board/udoo/neo/neo.c
+++ b/board/udoo/neo/neo.c
@@ -15,6 +15,7 @@
 #include <asm/arch/mx6-pins.h>
 #include <asm/gpio.h>
 #include <asm/mach-imx/iomux-v3.h>
+#include <env.h>
 #include <mmc.h>
 #include <fsl_esdhc_imx.h>
 #include <asm/arch/crm_regs.h>