lillipup: provide additional VBT for lillipup OLED sku

Lillipup add two sku for OLED panel.

Additional VBT is necessary to modify PWM source from VESA eDP AUX
interface

BUG=b:183630802
TEST=emerge-volteer coreboot-private-files-baseboard-volteer
check vbt_oled.bin is under build folder and check in CPU log.

Cq-Depend: chrome-internal:3744227
Signed-off-by: Kevin Chang <kevin.chang@lcfc.corp-partner.google.com>
Change-Id: I576297b8296def3c37a01ae0223fa332aa9f02b1
Reviewed-on: https://review.coreboot.org/c/coreboot/+/52150
Reviewed-by: Tim Wawrzynczak <twawrzynczak@chromium.org>
Reviewed-by: Zhuohao Lee <zhuohao@google.com>
Reviewed-by: YH Lin <yueherngl@google.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

src/mainboard/google/volteer/variants/baseboard/devicetree.cb

@@ -68,6 +68,10 @@ fw_config
 		option WIFI_SAR_ID_2 2
 		option WIFI_SAR_ID_3 3
 	end
+	field OLED_SCREEN 28
+		option OLED_NOT_PRESENT 0
+		option OLED_PRESENT 1
+	end
 end
 
 chip soc/intel/tigerlake

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

@@ -2,6 +2,7 @@
 
 #include <fw_config.h>
 #include <sar.h>
+#include <drivers/intel/gma/opregion.h>
 
 const char *get_wifi_sar_cbfs_filename(void)
 {
@@ -12,3 +13,10 @@ const char *get_wifi_sar_cbfs_filename(void)
 
 	return WIFI_SAR_CBFS_DEFAULT_FILENAME;
 }
+
+const char *mainboard_vbt_filename(void)
+{
+	if (fw_config_probe(FW_CONFIG(OLED_SCREEN, OLED_PRESENT)))
+		return "vbt-oled.bin";
+	return "vbt.bin";
+}