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/technologic/ts4800/ts4800.c b/board/technologic/ts4800/ts4800.c
index 927a19d..38d3a3d 100644
--- a/board/technologic/ts4800/ts4800.c
+++ b/board/technologic/ts4800/ts4800.c
@@ -11,6 +11,7 @@
 #include <asm/gpio.h>
 #include <asm/arch/imx-regs.h>
 #include <asm/arch/iomux-mx51.h>
+#include <env.h>
 #include <linux/errno.h>
 #include <asm/arch/sys_proto.h>
 #include <asm/arch/crm_regs.h>