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/keymile/common/ivm.c b/board/keymile/common/ivm.c
index 23bd21c..da0634f 100644
--- a/board/keymile/common/ivm.c
+++ b/board/keymile/common/ivm.c
@@ -6,6 +6,7 @@
 
 #include <common.h>
 #include <cli_hush.h>
+#include <env.h>
 #include <i2c.h>
 #include "common.h"