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/cmd/sf.c b/cmd/sf.c
index e993b3e..2b9c268 100644
--- a/cmd/sf.c
+++ b/cmd/sf.c
@@ -8,6 +8,7 @@
 #include <common.h>
 #include <div64.h>
 #include <dm.h>
+#include <flash.h>
 #include <malloc.h>
 #include <mapmem.h>
 #include <spi.h>