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/xpedite537x.h b/include/configs/xpedite537x.h
index 6d847cb..7262c86 100644
--- a/include/configs/xpedite537x.h
+++ b/include/configs/xpedite537x.h
@@ -47,6 +47,7 @@
 #define CONFIG_VERY_BIG_RAM
 
 #ifndef __ASSEMBLY__
+#include <linux/stringify.h>
 extern unsigned long get_board_sys_clk(unsigned long dummy);
 extern unsigned long get_board_ddr_clk(unsigned long dummy);
 #endif