mb/google/brya/var/kano: Add stylus probe

Kano has non-stylus sku. Add a FW_CONFIG field to indicate
stylus presence and add a probe statement to the devicetree for the
corresponding device.

BUG=b:208179467
TEST=non-stylus doesn't register garage driver.

Signed-off-by: David Wu <david_wu@quanta.corp-partner.google.com>
Change-Id: I24839c39280185a6d649a82dd9f025ee305c2eed
Reviewed-on: https://review.coreboot.org/c/coreboot/+/60389
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Tim Wawrzynczak <twawrzynczak@chromium.org>
diff --git a/src/mainboard/google/brya/variants/kano/overridetree.cb b/src/mainboard/google/brya/variants/kano/overridetree.cb
index a7e4271..87148c5 100644
--- a/src/mainboard/google/brya/variants/kano/overridetree.cb
+++ b/src/mainboard/google/brya/variants/kano/overridetree.cb
@@ -11,6 +11,10 @@
 		option UFC_USB			0
 		option UFC_MIPI_OVTI2740	1
 	end
+	field STYLUS 6
+		option STYLUS_ABSENT		0
+		option STYLUS_PRESENT		1
+	end
 end
 chip soc/intel/alderlake
 	register "SaGv" = "SaGv_Enabled"
@@ -440,7 +444,9 @@
 				register "key.linux_code" = "SW_PEN_INSERTED"
 				register "key.linux_input_type" = "EV_SW"
 				register "key.label" = ""pen_eject""
-				device generic 0 on end
+				device generic 0 on
+					probe STYLUS STYLUS_PRESENT
+				end
 			end
 		end
 		device ref i2c5 on