mb/google/volteer/var/volteer: add specific wifi SAR for volta

volta will use different wifi SAR from voxel.
Using clamshell mode of fw config to decide to load volta wifi sar.

BUG=b:184820057
TEST=build and verify wifi power as expect.

Cq-Depend: chrome-internal:3824093
Signed-off-by: Sheng-Liang Pan <sheng-liang.pan@quanta.corp-partner.google.com>
Change-Id: I000aefca63346c70556688f232ca54360b3badef
Reviewed-on: https://review.coreboot.org/c/coreboot/+/54051
Reviewed-by: Paul Fagerburg <pfagerburg@chromium.org>
Reviewed-by: YH Lin <yueherngl@google.com>
Reviewed-by: Tim Wawrzynczak <twawrzynczak@chromium.org>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

src/mainboard/google/volteer/Kconfig.name

@@ -65,6 +65,7 @@ config BOARD_GOOGLE_VOLTEER2_TI50
 config BOARD_GOOGLE_VOXEL
 	bool "-> Voxel"
 	select BOARD_GOOGLE_BASEBOARD_VOLTEER
+	select GEO_SAR_ENABLE if CHROMEOS_WIFI_SAR
 
 config BOARD_GOOGLE_ELEMI
 	bool "-> Elemi"

src/mainboard/google/volteer/variants/voxel/Makefile.inc

@@ -6,3 +6,4 @@ romstage-y += memory.c
 
 ramstage-y += gpio.c
 ramstage-y += ramstage.c
+ramstage-y += variant.c

src/mainboard/google/volteer/variants/voxel/variant.c

@@ -0,0 +1,14 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+
+#include <fw_config.h>
+#include <sar.h>
+
+const char *get_wifi_sar_cbfs_filename(void)
+{
+	const char *filename = NULL;
+
+	if (fw_config_probe(FW_CONFIG(TABLETMODE, TABLETMODE_DISABLED)))
+		filename = "wifi_sar-volta.hex";
+
+	return filename;
+}