env: Move env_set_ulong() to env.h

Move env_set_ulong() over to the new header file.

Signed-off-by: Simon Glass <sjg@chromium.org>
Acked-by: Joe Hershberger <joe.hershberger@ni.com>
diff --git a/board/gdsys/mpc8308/gazerbeam.c b/board/gdsys/mpc8308/gazerbeam.c
index cd62174..ddd6ee8 100644
--- a/board/gdsys/mpc8308/gazerbeam.c
+++ b/board/gdsys/mpc8308/gazerbeam.c
@@ -8,6 +8,7 @@
 #include <common.h>
 #include <board.h>
 #include <dm.h>
+#include <env.h>
 #include <fdt_support.h>
 #include <fsl_esdhc.h>
 #include <miiphy.h>