util/mainboard/google: add support for Volteer

create_coreboot_variant.sh now supports the Volteer baseboard in
addition to Hatch. The shell script and supporting python code are
moved up one level, while retaining the ${BASE}/template/* file
structure for each supported baseboard.

kconfig.py has to add slightly different text to Kconfig.name
depending on which baseboard is selected.

BRANCH=None
BUG=b:146646594
TEST=Create variants of Hatch and Volteer, check that the staged
commits are correct.

$ ./create_coreboot_variant.sh hatch sushi b:12345
src/mainboard/google/hatch/Kconfig and Kconfig.name will have new
sections for SUSHI. src/mainboard/google/hatch/variants/sushi
will have a copy of util/mainboard/google/hatch/template

$ ./create_coreboot_variant.sh volteer ripto b:12345
src/mainboard/google/volteer/Kconfig and Kconfig.name will have new
sections for RIPTO. src/mainboard/google/volteer/variants/ripto
will have a copy of util/mainboard/google/volteer/template

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

Change-Id: I084b6c50bb76af0d11dc86a96b3c3c434569a0dd
Signed-off-by: Paul Fagerburg <pfagerburg@chromium.org>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/37878
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Justin TerAvest <teravest@chromium.org>
Reviewed-by: Marco Chen <marcochen@google.com>

util/mainboard/google/volteer/template/Makefile.inc

@@ -0,0 +1,13 @@
+## This file is part of the coreboot project.
+##
+## This program is free software; you can redistribute it and/or modify
+## it under the terms of the GNU General Public License as published by
+## the Free Software Foundation; version 2 of the License.
+##
+## This program is distributed in the hope that it will be useful,
+## but WITHOUT ANY WARRANTY; without even the implied warranty of
+## MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+## GNU General Public License for more details.
+##
+
+SPD_SOURCES =