mb/google/nissa/var/xivu: Add gpio.c to ramstage

Fixes a bug in Makefile.inc.

BUG=b:236576117
BRANCH=None
TEST=emerge-nissa coreboot

Signed-off-by: Ian Feng <ian_feng@compal.corp-partner.google.com>
Change-Id: I2664df961a1fc0cd904a5e742face20c3fc8c3c9
Reviewed-on: https://review.coreboot.org/c/coreboot/+/65450
Reviewed-by: Reka Norman <rekanorman@chromium.org>
Reviewed-by: Frank Wu <frank_wu@compal.corp-partner.google.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

src/mainboard/google/brya/variants/xivu/Makefile.inc

@@ -2,3 +2,5 @@
 bootblock-y += gpio.c
 
 romstage-y += gpio.c
+
+ramstage-y += gpio.c