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/cmd/nand.c b/cmd/nand.c
index 9c2b5d7..c42ab24 100644
--- a/cmd/nand.c
+++ b/cmd/nand.c
@@ -20,6 +20,7 @@
  */
 
 #include <common.h>
+#include <bootstage.h>
 #include <image.h>
 #include <asm/cache.h>
 #include <linux/mtd/mtd.h>