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/xpedite550x.h b/include/configs/xpedite550x.h
index 106269b..b9c9ac4 100644
--- a/include/configs/xpedite550x.h
+++ b/include/configs/xpedite550x.h
@@ -46,6 +46,7 @@
 #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