common: Drop bootstage.h from common header

Move this fairly uncommon header out of the common header.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/board/buffalo/lsxl/lsxl.c b/board/buffalo/lsxl/lsxl.c
index aa64125..56a2c29 100644
--- a/board/buffalo/lsxl/lsxl.c
+++ b/board/buffalo/lsxl/lsxl.c
@@ -8,6 +8,7 @@
  */
 
 #include <common.h>
+#include <bootstage.h>
 #include <env.h>
 #include <env_internal.h>
 #include <flash.h>