env: Move env_relocate() to env.h

Move env_relocate() 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/env/common.c b/env/common.c
index bd340fe..1fbc4a8 100644
--- a/env/common.c
+++ b/env/common.c
@@ -9,6 +9,7 @@
 
 #include <common.h>
 #include <command.h>
+#include <env.h>
 #include <environment.h>
 #include <linux/stddef.h>
 #include <search.h>