hatch: automate creating a new variant in coreboot

To create a new variant of the hatch baseboard, we need to
add the variant's GBB_HWID and other information to Kconfig
and Kconfig.name, and set up a skeletal build based on the
hatch baseboard.

BUG=b:140261109
BRANCH=none
TEST=``./create_coreboot_variant.sh sushi && git show``
Kconfig will have three new lines for the SUSHI variant, and
Kconfig.name will have an entirely new section.
New files created are:
variants/sushi/Makefile.inc
variants/sushi/overridetree.cb
variants/sushi/include/ec.h
variants/sushi/include/gpio.h
variants/sushi/include/variant/acpi/dptf.asl

Also run the script with an existing board name to verify that you
can't create a variant that already exists.

Change-Id: I1a5b9c8735faafebb2e4e384cb3346867d64c556
Signed-off-by: Paul Fagerburg <pfagerburg@chromium.org>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/35239
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Furquan Shaikh <furquan@google.com>

util/mainboard/google/hatch/template/overridetree.cb

@@ -0,0 +1,6 @@
+chip soc/intel/cannonlake
+
+	device domain 0 on
+	end
+
+end