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/arm/lib/bootm.c b/arch/arm/lib/bootm.c
index dc845a9..c189bdc 100644
--- a/arch/arm/lib/bootm.c
+++ b/arch/arm/lib/bootm.c
@@ -12,6 +12,7 @@
  */
 
 #include <common.h>
+#include <bootstage.h>
 #include <command.h>
 #include <cpu_func.h>
 #include <dm.h>