mb/google/skyrim: Create winterhold variant

Create the winterhold variant of the skyrim 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:240970782
BRANCH=None
TEST=util/abuild/abuild -p none -t google/skyrim -x -a
make sure the build includes GOOGLE_WINTERHOLD

Signed-off-by: Isaac Lee <isaaclee@google.com>
Change-Id: I0e16f0a674aa3f4687cd82d5840a3c2087148a51
Reviewed-on: https://review.coreboot.org/c/coreboot/+/66620
Reviewed-by: Karthik Ramasubramanian <kramasub@google.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

src/mainboard/google/skyrim/Kconfig

@@ -65,6 +65,7 @@ config MAINBOARD_FAMILY
 
 config MAINBOARD_PART_NUMBER
 	default "Skyrim" if BOARD_GOOGLE_SKYRIM
+	default "Winterhold" if BOARD_GOOGLE_WINTERHOLD
 
 config OVERRIDE_DEVICETREE
 	string
@@ -73,6 +74,7 @@ config OVERRIDE_DEVICETREE
 config VARIANT_DIR
 	string
 	default "skyrim" if BOARD_GOOGLE_SKYRIM
+	default "winterhold" if BOARD_GOOGLE_WINTERHOLD
 
 config VBOOT
 	select VBOOT_LID_SWITCH