dt-bindings: input: sun4i-lradc: Add wakeup-source

The LRADC can be a wakeup source and is listed as such in some DT
already. Let's make sure we allow that property in the binding.
Signed-off-by: Maxime Ripard <maxime@cerno.tech>
Reviewed-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20210721140424.725744-21-maxime@cerno.techSigned-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>

Documentation/devicetree/bindings/input/allwinner,sun4i-a10-lradc-keys.yaml

@@ -29,6 +29,8 @@ properties:
     description:
       Regulator for the LRADC reference voltage
 
+  wakeup-source: true
+
 patternProperties:
   "^button-[0-9]+$":
     type: object