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

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

···
   linux,keycodes:
     maxItems: 1
 
+  wakeup-source: true
+
 required:
   - compatible
   - linux,keycodes