mb/google/nissa/var/nivviks: enable WIFI_SAR

Add get_wifi_sar_cbfs_filename().  This function uses the FW_CONFIG
for WIFI_CATEGORY to choose the right wifi_sar hex file.

Below is the file mapping:
    wifi_sar_0.hex = wifi6
    wifi_sar_1.hex = wifi7

BUG=b:345596420
TEST=emerge-nissa coreboot chromeos-bootimage

Cq-Depend: chrome-internal:7607427
Change-Id: If8339a2a1d32d3e885ef87ea2ec2847f107f1fbd
Signed-off-by: David Wu <david_wu@quanta.corp-partner.google.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/84051
Reviewed-by: Subrata Banik <subratabanik@google.com>
Reviewed-by: Eric Lai <ericllai@google.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

src/mainboard/google/brya/Kconfig

@@ -355,6 +355,7 @@ config BOARD_GOOGLE_MOLI
 config BOARD_GOOGLE_NIVVIKS
 	select BOARD_GOOGLE_BASEBOARD_NISSA
 	select BOARD_ROMSIZE_KB_32768
+	select CHROMEOS_WIFI_SAR if CHROMEOS
 	select DRIVERS_GENERIC_GPIO_KEYS
 	select DRIVERS_GENESYSLOGIC_GL9750
 	select DRIVERS_I2C_SX9324
@@ -552,6 +553,7 @@ config BOARD_GOOGLE_TEREID
 config BOARD_GOOGLE_TIVVIKS
 	select BOARD_GOOGLE_BASEBOARD_NISSA
 	select BOARD_ROMSIZE_KB_32768
+	select CHROMEOS_WIFI_SAR if CHROMEOS
 	select DRIVERS_GENERIC_GPIO_KEYS
 	select DRIVERS_GENESYSLOGIC_GL9750
 	select DRIVERS_I2C_SX9324

src/mainboard/google/brya/variants/nivviks/Makefile.mk

@@ -5,4 +5,5 @@ romstage-y += gpio.c
 romstage-y += memory.c
 
 ramstage-$(CONFIG_FW_CONFIG) += fw_config.c
+ramstage-$(CONFIG_FW_CONFIG) += variant.c
 ramstage-y += gpio.c

src/mainboard/google/brya/variants/nivviks/variant.c

@@ -0,0 +1,9 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+
+#include <fw_config.h>
+#include <sar.h>
+
+const char *get_wifi_sar_cbfs_filename(void)
+{
+	return get_wifi_sar_fw_config_filename(FW_CONFIG_FIELD(WIFI_CATEGORY));
+}