dt-bindings: gpio: ds4520: Add ADI DS4520

Add ADI DS4520 devicetree document.
Signed-off-by: Okan Sahin <okan.sahin@analog.com>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>

Documentation/devicetree/bindings/gpio/adi,ds4520-gpio.yaml

+# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/gpio/adi,ds4520-gpio.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: DS4520 I2C GPIO expander
+
+maintainers:
+  - Okan Sahin <okan.sahin@analog.com>
+
+properties:
+  compatible:
+    enum:
+      - adi,ds4520-gpio
+
+  reg:
+    maxItems: 1
+
+  gpio-controller: true
+
+  "#gpio-cells":
+    const: 2
+
+  ngpios:
+    minimum: 1
+    maximum: 9
+
+required:
+  - compatible
+  - reg
+  - gpio-controller
+  - "#gpio-cells"
+  - ngpios
+
+additionalProperties: false
+
+examples:
+  - |
+    i2c {
+        #address-cells = <1>;
+        #size-cells = <0>;
+
+        gpio@50 {
+            compatible = "adi,ds4520-gpio";
+            reg = <0x50>;
+            ngpios = <9>;
+            gpio-controller;
+            #gpio-cells = <2>;
+        };
+    };