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/bachmann/ot1200/ot1200.c b/board/bachmann/ot1200/ot1200.c
index 067a970..36f3708 100644
--- a/board/bachmann/ot1200/ot1200.c
+++ b/board/bachmann/ot1200/ot1200.c
@@ -9,6 +9,7 @@
 #include <asm/arch/clock.h>
 #include <asm/arch/imx-regs.h>
 #include <asm/arch/iomux.h>
+#include <env.h>
 #include <malloc.h>
 #include <asm/arch/mx6-pins.h>
 #include <asm/mach-imx/iomux-v3.h>