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/x86/lib/bootm.c b/arch/x86/lib/bootm.c
index 07d8f1f..0837655 100644
--- a/arch/x86/lib/bootm.c
+++ b/arch/x86/lib/bootm.c
@@ -8,6 +8,7 @@
  */
 
 #include <common.h>
+#include <bootstage.h>
 #include <command.h>
 #include <hang.h>
 #include <dm/device.h>