dt-bindings: gpio: pca9570: Add label property

Add a label property to allow a custom name to be used for identifying
a device on the board. This is useful when multiple devices are present on
the same board. Similar change was done by commit ffae65fb
("dt-bindings: spi: spi-cadence: Add label property") or by commit
a53faa6bfa3b ("dt-bindings: hwmon: ina2xx: Add label property").
Signed-off-by: Michal Simek <michal.simek@amd.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>

Documentation/devicetree/bindings/gpio/gpio-pca9570.yaml

@@ -28,6 +28,9 @@ properties:
     minItems: 4
     maxItems: 8
 
+  label:
+    description: A descriptive name for this device.
+
 required:
   - compatible
   - reg