mb/google/nissa/var/anraggar: add FW config to apply the wifi sar

1.In contrast to the MediaTek Wi-Fi module, the Intel Wi-Fi module needs
 to load a SAR table.

2.Describe the FW_CONFIG probe for the settings.
- WIFI_6 for MTK Wi-Fi module MT7921L
- WIFI_6E for Intel Wi-Fi module AX211NGW

BUG=b:315418153
TEST=emerge-nissa coreboot

Change-Id: I37e8adc3de02707b2df541cc5e6f88083554eeb4
Signed-off-by: Jianeng Ceng <cengjianeng@huaqin.corp-partner.google.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/79858
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Eric Lai <ericllai@google.com>
Reviewed-by: Weimin Wu <wuweimin@huaqin.corp-partner.google.com>

src/mainboard/google/brya/variants/anraggar/overridetree.cb

@@ -1,4 +1,9 @@
 fw_config
+	field WIFI 10 11
+		option UNKNOWN		0
+		option WIFI_6		1
+		option WIFI_6E		2
+	end
 	field CAMERA 12 13
 		option UF_720P_WF		0
 		option UF_1080P			1

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

@@ -1,8 +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 "wifi_sar_2.hex";
+	return get_wifi_sar_fw_config_filename(FW_CONFIG_FIELD(WIFI));
 }