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/B4860QDS.h b/include/configs/B4860QDS.h
index 6763945..a515bf9 100644
--- a/include/configs/B4860QDS.h
+++ b/include/configs/B4860QDS.h
@@ -6,6 +6,8 @@
 #ifndef __CONFIG_H
 #define __CONFIG_H
 
+#include <linux/stringify.h>
+
 /*
  * B4860 QDS board configuration file
  */