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/M54418TWR.h b/include/configs/M54418TWR.h
index cdf169f..2866bfd 100644
--- a/include/configs/M54418TWR.h
+++ b/include/configs/M54418TWR.h
@@ -13,6 +13,8 @@
 #ifndef _M54418TWR_H
 #define _M54418TWR_H
 
+#include <linux/stringify.h>
+
 /*
  * High Level Configuration Options
  * (easy to change)