mainboard/google/poppy: Add variant API for board_id and gpio

Provide APIs for board_id() and gpio table functionality. Default weak
implementations are provided from the baseboard.

BUG=b:37375693

Change-Id: Ic3c946e6cb12b3c8ef3e83a1037ed0fc8cffbded
Signed-off-by: Furquan Shaikh <furquan@chromium.org>
Reviewed-on: https://review.coreboot.org/19323
Tested-by: build bot (Jenkins)
Reviewed-by: Aaron Durbin <adurbin@chromium.org>
8 files changed