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/drivers/fastboot/fb_nand.c b/drivers/fastboot/fb_nand.c
index 6756ea7..b165468 100644
--- a/drivers/fastboot/fb_nand.c
+++ b/drivers/fastboot/fb_nand.c
@@ -6,6 +6,7 @@
 
 #include <config.h>
 #include <common.h>
+#include <flash.h>
 
 #include <fastboot.h>
 #include <image-sparse.h>