common: Drop linux/stringify.h from common header

Move this uncommon header out of the common header.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/include/configs/MPC8308RDB.h b/include/configs/MPC8308RDB.h
index f55e9a0..788a325 100644
--- a/include/configs/MPC8308RDB.h
+++ b/include/configs/MPC8308RDB.h
@@ -8,6 +8,8 @@
 #ifndef __CONFIG_H
 #define __CONFIG_H
 
+#include <linux/stringify.h>
+
 /*
  * High Level Configuration Options
  */