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/alliedtelesis/x530/x530.c b/board/alliedtelesis/x530/x530.c
index 97dbed7..e0fa806 100644
--- a/board/alliedtelesis/x530/x530.c
+++ b/board/alliedtelesis/x530/x530.c
@@ -6,6 +6,7 @@
 #include <common.h>
 #include <command.h>
 #include <dm.h>
+#include <env.h>
 #include <i2c.h>
 #include <wdt.h>
 #include <asm/gpio.h>