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/spear/x600/x600.c b/board/spear/x600/x600.c
index e1232ed..7cff6ee 100644
--- a/board/spear/x600/x600.c
+++ b/board/spear/x600/x600.c
@@ -7,6 +7,7 @@
  */
 
 #include <common.h>
+#include <flash.h>
 #include <init.h>
 #include <micrel.h>
 #include <nand.h>