dt-bindings: input: fsl,scu-key: Document wakeup-source

The SCU Key controller can be used as a system wakeup source.

Document the 'wakeup-source' property.

This fixes the following schema warning:

system-controller: keys: 'wakeup-source' does not match any of the regexes: 'pinctrl-[0-9]+'
	from schema $id: http://devicetree.org/schemas/firmware/fsl,scu.yaml#Signed-off-by: Fabio Estevam <festevam@denx.de>
Acked-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20230926122957.341094-1-festevam@gmail.comSigned-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>

Documentation/devicetree/bindings/input/fsl,scu-key.yaml

@@ -24,6 +24,8 @@ properties:
   linux,keycodes:
     maxItems: 1
 
+  wakeup-source: true
+
 required:
   - compatible
   - linux,keycodes