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/isee/igep00x0/igep00x0.c b/board/isee/igep00x0/igep00x0.c
index 367af82..74fc5f0 100644
--- a/board/isee/igep00x0/igep00x0.c
+++ b/board/isee/igep00x0/igep00x0.c
@@ -4,6 +4,7 @@
  * ISEE 2007 SL, <www.iseebcn.com>
  */
 #include <common.h>
+#include <env.h>
 #include <status_led.h>
 #include <dm.h>
 #include <ns16550.h>