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/board/renesas/lager/lager.c b/board/renesas/lager/lager.c
index f062bb0..bda3295 100644
--- a/board/renesas/lager/lager.c
+++ b/board/renesas/lager/lager.c
@@ -8,6 +8,7 @@
  */
 
 #include <common.h>
+#include <env.h>
 #include <environment.h>
 #include <malloc.h>
 #include <netdev.h>