common: Drop flash.h from common header

Move this uncommon header out of the common header.

Fix up some style problems in flash.h while we are here.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/board/gdsys/mpc8308/strider.c b/board/gdsys/mpc8308/strider.c
index 9ba9e42..a12e086 100644
--- a/board/gdsys/mpc8308/strider.c
+++ b/board/gdsys/mpc8308/strider.c
@@ -6,6 +6,7 @@
 
 #include <common.h>
 #include <env.h>
+#include <flash.h>
 #include <hwconfig.h>
 #include <i2c.h>
 #include <init.h>