dt-bindings: input: matrix_keypad - add wakeup-source property

The driver recognizes standard "wakeup-source" property and there are
DTS files using it. Add the property to the binding.

Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202502280105.REZ29MVg-lkp@intel.com/
Reviewed-by: Manuel Traut <manuel.traut@mt.com>
Acked-by: Conor Dooley <conor.dooley@microchip.com>
Link: https://lore.kernel.org/r/Z8EMI9ALqYY72VBV@google.com
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>

Documentation/devicetree/bindings/input/gpio-matrix-keypad.yaml

@@ -68,6 +68,8 @@ properties:
       Drive inactive columns during scan,
       default is to turn inactive columns into inputs.
 
+  wakeup-source: true
+
 required:
   - compatible
   - row-gpios
@@ -96,4 +98,6 @@ examples:
                         0x0001006A
                         0x0101001C
                         0x0201006C>;
+
+        wakeup-source;
     };