dt-bindings: input: touchscreen: edt-ft5x06: Add 'threshold' property

Add a new property 'threshold' to the edt-ft5x06 touchscreen binding.
This property allows setting the "click"-threshold in the range from 0
to 255. This change addresses the following dtbs_check warning:
imx6dl-lanmcu.dtb: touchscreen@38: 'threshold' does not match any of the regexes: 'pinctrl-[0-9]+'
Signed-off-by: Oleksij Rempel <o.rempel@pengutronix.de>
Reviewed-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20230621093245.78130-6-o.rempel@pengutronix.deSigned-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>

Documentation/devicetree/bindings/input/touchscreen/edt-ft5x06.yaml

@@ -93,6 +93,12 @@ properties:
     minimum: 1
     maximum: 255
 
+  threshold:
+    description: Allows setting the  "click"-threshold in the range from 0 to 255.
+    $ref: /schemas/types.yaml#/definitions/uint32
+    minimum: 0
+    maximum: 255
+
   touchscreen-size-x: true
   touchscreen-size-y: true
   touchscreen-fuzz-x: true