env: Move env_get_ulong() to env.h

Move env_get_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/toradex/colibri_imx6/colibri_imx6.c b/board/toradex/colibri_imx6/colibri_imx6.c
index 6417ba4..f657db8 100644
--- a/board/toradex/colibri_imx6/colibri_imx6.c
+++ b/board/toradex/colibri_imx6/colibri_imx6.c
@@ -8,6 +8,7 @@
 
 #include <common.h>
 #include <dm.h>
+#include <env.h>
 
 #include <asm/arch/clock.h>
 #include <asm/arch/crm_regs.h>