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/apf27.h b/include/configs/apf27.h
index c26cf89..cecd485 100644
--- a/include/configs/apf27.h
+++ b/include/configs/apf27.h
@@ -9,6 +9,8 @@
 #ifndef __CONFIG_H
 #define __CONFIG_H
 
+#include <linux/stringify.h>
+
 #define CONFIG_ENV_VERSION	10
 #define CONFIG_BOARD_NAME apf27