dt-bindings: gpio: Add gpio-line-names to STMPE GPIO

This is a gpio-controller, so gpio-line-names should be allowed as well.
stmpe2403 supports up to 24 GPIOs.
Signed-off-by: Alexander Stein <alexander.stein@ew.tq-group.com>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>

Documentation/devicetree/bindings/gpio/st,stmpe-gpio.yaml

@@ -28,6 +28,10 @@ properties:
 
   gpio-controller: true
 
+  gpio-line-names:
+    minItems: 1
+    maxItems: 24
+
   interrupt-controller: true
 
   st,norequest-mask: