proto: Add new field servo_fw_channel

New servo fw can have stable, prev, dev, alpha channels.

BUG=b:181711016
TEST=None

Change-Id: Id7c84ff3b774255fc2b010639f383296123005d3
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/infra/proto/+/2730861
Auto-Submit: Otabek Kasimov <otabek@google.com>
Reviewed-by: Eshwar Narayan <eshwarn@chromium.org>
Reviewed-by: Xixuan Wu <xixuan@chromium.org>
Commit-Queue: Otabek Kasimov <otabek@google.com>
2 files changed