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/mx6_common.h b/include/configs/mx6_common.h
index 07b1e06..0715509 100644
--- a/include/configs/mx6_common.h
+++ b/include/configs/mx6_common.h
@@ -6,6 +6,8 @@
 #ifndef __MX6_COMMON_H
 #define __MX6_COMMON_H
 
+#include <linux/stringify.h>
+
 #if (defined(CONFIG_MX6UL) || defined(CONFIG_MX6ULL))
 #define CONFIG_SC_TIMER_CLK 8000000 /* 8Mhz */
 #define COUNTER_FREQUENCY CONFIG_SC_TIMER_CLK