dt-bindings: touchscreen: resistive-adc-touch: change to unevaluatedProperties

Change additionalProperties to unevaluatedProperties because it refs to
touchscreen.yaml.

Fix below CHECK_DTBS warnings:
arch/arm/boot/dts/nxp/imx/imx6dl-skov-revc-lt6.dtb: touchscreen (resistive-adc-touch): 'touchscreen-y-plate-ohms' does not match any of the regexes: '^pinctrl-[0-9]+$'
from schema $id: http://devicetree.org/schemas/input/touchscreen/resistive-adc-touch.yaml#

Signed-off-by: Frank Li <[e-mail]>
Acked-by: Rob Herring (Arm) <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Dmitry Torokhov <[e-mail]>

Documentation/devicetree/bindings/input/touchscreen/resistive-adc-touch.yaml

···
   touchscreen-min-pressure: true
   touchscreen-x-plate-ohms: true
 
-additionalProperties: false
+unevaluatedProperties: false
 
 required:
   - compatible