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/arch/nds32/lib/bootm.c b/arch/nds32/lib/bootm.c
index 1003bc8..b173686 100644
--- a/arch/nds32/lib/bootm.c
+++ b/arch/nds32/lib/bootm.c
@@ -6,6 +6,7 @@
  */
 
 #include <common.h>
+#include <bootstage.h>
 #include <command.h>
 #include <env.h>
 #include <hang.h>