mb/google/brya: Create yavilla variant

mb/google/brya: Create yavilla variant

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

(Auto-Generated by create_coreboot_variant.sh version 4.5.0).

BUG=b:273791621
BRANCH=firmware-nissa-15217.B
TEST=util/abuild/abuild -p none -t google/brya -x -a
make sure the build includes GOOGLE_YAVILLA

Change-Id: I4539090da5e1db474a8f58a42aecc38659959f75
Signed-off-by: Tony Huang <tony-huang@quanta.corp-partner.google.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/73721
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Eric Lai <eric_lai@quanta.corp-partner.google.com>