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/misc/fs_loader.c b/drivers/misc/fs_loader.c
index f42eeff..88e486e 100644
--- a/drivers/misc/fs_loader.c
+++ b/drivers/misc/fs_loader.c
@@ -5,6 +5,7 @@
  */
 #include <common.h>
 #include <dm.h>
+#include <env.h>
 #include <errno.h>
 #include <blk.h>
 #include <fs.h>