dt-bindings: gpio: add fcs,fxl6408

Add Fairchild FXL6408 8-bit I2C-controlled GPIO expander.

Signed-off-by: Emanuele Ghidoli <[e-mail]>
Signed-off-by: Francesco Dolcini <[e-mail]>
Reviewed-by: Krzysztof Kozlowski <[e-mail]>
Reviewed-by: Linus Walleij <[e-mail]>
Signed-off-by: Bartosz Golaszewski <[e-mail]>

Documentation/devicetree/bindings/gpio/fcs,fxl6408.yaml

···
+# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/gpio/fcs,fxl6408.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Fairchild FXL6408 I2C GPIO Expander
+
+maintainers:
+  - Emanuele Ghidoli <[e-mail]>
+
+properties:
+  compatible:
+    enum:
+      - fcs,fxl6408
+
+  reg:
+    maxItems: 1
+
+  "#gpio-cells":
+    const: 2
+
+  gpio-controller: true
+
+  gpio-line-names:
+    minItems: 1
+    maxItems: 8
+
+patternProperties:
+  "^(hog-[0-9]+|.+-hog(-[0-9]+)?)$":
+    required:
+      - gpio-hog
+
+required:
+  - compatible
+  - reg
+  - gpio-controller
+  - "#gpio-cells"
+
+additionalProperties: false
+
+examples:
+  - |
+    i2c {
+        #address-cells = <1>;
+        #size-cells = <0>;
+
+        gpio_expander_43: gpio-expander@43 {
+            compatible = "fcs,fxl6408";
+            reg = <0x43>;
+            gpio-controller;
+            #gpio-cells = <2>;
+            gpio-line-names = "Wi-Fi_W_DISABLE", "Wi-Fi_WKUP_WLAN",
+                              "PWR_EN_+V3.3_WiFi_N", "PCIe_REF_CLK_EN",
+                              "USB_RESET_N", "USB_BYPASS_N", "Wi-Fi_PDn",
+                              "Wi-Fi_WKUP_BT";
+        };
+    };