cros_ec: Add cros_ec_build_info and callback

Wilco does not expose the fw version via the RO or RW version like a
standard CROS EC. Instead we will use the build info.

The function is marked as unused because it will be used in the next cl.

BUG=b:130438917
TEST=mosys ish info on Sarien

Change-Id: I3500b076d0c8ba63a732e0fd4b636a2a92e3f9da
Signed-off-by: Raul E Rangel <rrangel@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/1625451
Commit-Ready: ChromeOS CL Exonerator Bot <chromiumos-cl-exonerator@appspot.gserviceaccount.com>
Legacy-Commit-Queue: Commit Bot <commit-bot@chromium.org>
Reviewed-by: Jett Rink <jettrink@chromium.org>
3 files changed