dt-bindings: input: matrix_keypad - add missing property

The property is implemented in the driver but not described in dt-bindings.
Add missing property 'gpio-activelow' to DT schema.

Signed-off-by: Markus Burri <markus.burri@mt.com>
Link: https://lore.kernel.org/r/20250226152843.43932-3-markus.burri@mt.com
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>

Author: Markus Burri

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

@@ -40,6 +40,11 @@ properties:
     type: boolean
     description: Do not enable autorepeat feature.
 
+  gpio-activelow:
+    type: boolean
+    description:
+      Force GPIO polarity to active low.
+      In the absence of this property GPIOs are treated as active high.
 
   debounce-delay-ms:
     description: Debounce interval in milliseconds.