env: Move env_get() to env.h

Move env_get() 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/drivers/video/mb862xx.c b/drivers/video/mb862xx.c
index 1a3c970..301c1f0 100644
--- a/drivers/video/mb862xx.c
+++ b/drivers/video/mb862xx.c
@@ -12,6 +12,7 @@
 #include <common.h>
 
 #include <asm/io.h>
+#include <env.h>
 #include <pci.h>
 #include <video_fb.h>
 #include "videomodes.h"