util/mb/google/tmpl/puff: Generate correct gpio muxing

BUG=b:154071868
BRANCH=none
TEST=none

Change-Id: Iae4fe48b6a3df730b2334cb1f32b35addc90bec0
Signed-off-by: Edward O'Callaghan <quasisec@google.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/42674
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Sam McNally <sammc@google.com>
Reviewed-by: Paul Fagerburg <pfagerburg@chromium.org>

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

@@ -1,4 +1,4 @@
-##
 ## SPDX-License-Identifier: GPL-2.0-only
 
-SPD_SOURCES =
+ramstage-y += gpio.c
+bootblock-y += gpio.c