vendorcode/google: add common smbios mainboard version support

Provide an option to deliver the mainboard smbios version in the
form of 'rev%d' based on the board_id() value.

BUG=chromium:663243

Change-Id: If0a34935f570612da6e0c950fd7e8f0d92b6984f
Signed-off-by: Aaron Durbin <adurbin@chromium.org>
Reviewed-on: https://review.coreboot.org/17290
Reviewed-by: Furquan Shaikh <furquan@google.com>
Tested-by: build bot (Jenkins)
3 files changed