mb/google/volteer: Create drobit variant

mb/google/volteer: Create drobit variant

Create the drobit variant of the volteer reference board by copying
the template files to a new directory named for the variant.

(Auto-Generated by create_coreboot_variant.sh version 4.2.0).

BUG=b:171947885
BRANCH=none
TEST=emerge-volteer coreboot

Signed-off-by: Frank Chu <frank_chu@pegatron.corp-partner.google.com>
Change-Id: I63b7312bba236bd5af028359804d042f6850d8ba
Reviewed-on: https://review.coreboot.org/c/coreboot/+/47787
Reviewed-by: Zhuohao Lee <zhuohao@chromium.org>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>