mb/google/rex: Add FW_CONFIG for TOUCH over SPI

TEST=set the corresponding cbi bit, and saw SPI0 under sysfs
BUG=b:278783755

Signed-off-by: Eran Mitrani <mitrani@google.com>
Change-Id: I7099cde14cff90ad63e9164769f9913a8284a805
Reviewed-on: https://review.coreboot.org/c/coreboot/+/74888
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Subrata Banik <subratabanik@google.com>
Reviewed-by: Wonkyu Kim <wonkyu.kim@intel.com>
Reviewed-by: Kapil Porwal <kapilporwal@google.com>
diff --git a/src/mainboard/google/rex/variants/rex0/overridetree.cb b/src/mainboard/google/rex/variants/rex0/overridetree.cb
index 84a0b6a..d3062ad 100644
--- a/src/mainboard/google/rex/variants/rex0/overridetree.cb
+++ b/src/mainboard/google/rex/variants/rex0/overridetree.cb
@@ -42,6 +42,10 @@
 		option WIFI_CNVI		0
 		option WIFI_PCIE		1
 	end
+	field TOUCHSCREEN 19
+		option TOUCHSCREEN_I2C		0
+		option TOUCHSCREEN_I2C_SPI	1
+	end
 end
 
 chip soc/intel/meteorlake
@@ -75,7 +79,7 @@
 	}"
 
 	register "serial_io_gspi_mode" = "{
-		[PchSerialIoIndexGSPI0] = PchSerialIoDisabled,
+		[PchSerialIoIndexGSPI0] = PchSerialIoPci,
 		[PchSerialIoIndexGSPI1] = PchSerialIoPci,
 		[PchSerialIoIndexGSPI2] = PchSerialIoDisabled,
 	}"
@@ -705,6 +709,9 @@
 			end
 			probe DB_SD SD_GL9755S
 		end
+		device ref gspi0 on
+			probe TOUCHSCREEN TOUCHSCREEN_I2C_SPI
+		end
 		device ref gspi1 on
 			chip drivers/spi/acpi
 				register "name" = ""CRFP""