Add 'vfat' flag when building kernel with initramfs

We are about to separate VFAT support from 'initramfs' flag. Let's add
'vfat' flag first so that when this happens nothing gets broken.

BUG=chrome-os-partner:9805
TEST=Build success. Factory install shim still works.

Change-Id: Ia432e3b1a6186f4f7c817a1283c86066ced5fef1
Reviewed-on: https://gerrit.chromium.org/gerrit/23193
Reviewed-by: Hung-Te Lin <hungte@chromium.org>
Reviewed-by: Olof Johansson <olofj@chromium.org>
Commit-Ready: Vic Yang <victoryang@chromium.org>
Tested-by: Vic Yang <victoryang@chromium.org>
2 files changed