mb/google/dedede/var/cret: Modify Wifi SAR condition

Using tablet mode of fw config to decide to load custom wifi sar or not.

BUG=b:194163604
TEST=build and test on cret and cret360

Signed-off-by: Ian Feng <ian_feng@compal.corp-partner.google.com>
Change-Id: Ie94c2a07ad43fe1cb426e543dd97ed0434c42f2d
Reviewed-on: https://review.coreboot.org/c/coreboot/+/56968
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Henry Sun <henrysun@google.com>
Reviewed-by: Karthik Ramasubramanian <kramasub@google.com>

src/mainboard/google/dedede/variants/cret/variant.c

@@ -9,7 +9,12 @@
 
 const char *get_wifi_sar_cbfs_filename(void)
 {
-	return "wifi_sar-cret.hex";
+	const char *filename = NULL;
+
+	if (fw_config_probe(FW_CONFIG(TABLETMODE, TABLETMODE_ENABLED)))
+		filename = "wifi_sar-cret.hex";
+
+	return filename;
 }
 
 static void power_off_lte_module(void)