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/helios4.h b/include/configs/helios4.h
index f0ca8e2..671c3d2 100644
--- a/include/configs/helios4.h
+++ b/include/configs/helios4.h
@@ -7,6 +7,7 @@
 #define _CONFIG_HELIOS4_H
 
 #include <linux/sizes.h>
+#include <linux/stringify.h>
 
 /*
  * High Level Configuration Options (easy to change)