mb/google/hatch: Create kohaku variant

mb/google/hatch: Create kohaku variant

Creating Kohaku hatch variant.  Currently taking a copy of the hatch
variant.  Kohaku-specific changes to come in future CLs.

BUG=b:129706980
BRANCH=NONE
TEST=NONE

Change-Id: Ib4b8c2c8332910d992549e3aae8e6aff5234698b
Signed-off-by: Shelley Chen <shchen@google.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/32160
Reviewed-by: Furquan Shaikh <furquan@google.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>