dt-bindings: usb: Add binding for Genesys Logic GL850G hub controller

The Genesys Logic GL850G is a USB 2.0 Single TT hub controller that
features 4 downstream ports, an internal 5V-to-3.3V LDO regulator (can
be bypassed) and an external reset pin.

Add a device tree binding for its USB protocol part. The internal LDO is
not covered by this and can just be modelled as a fixed regulator.
Signed-off-by: Icenowy Zheng <uwu@icenowy.me>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://lore.kernel.org/r/20221206055228.306074-3-uwu@icenowy.meSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Documentation/devicetree/bindings/usb/genesys,gl850g.yaml

+# SPDX-License-Identifier: GPL-2.0-only or BSD-2-Clause
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/usb/genesys,gl850g.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Genesys Logic GL850G USB 2.0 hub controller
+
+maintainers:
+  - Icenowy Zheng <uwu@icenowy.me>
+
+allOf:
+  - $ref: usb-device.yaml#
+
+properties:
+  compatible:
+    enum:
+      - usb5e3,608
+
+  reg: true
+
+  reset-gpios:
+    description: GPIO controlling the RESET# pin.
+
+  vdd-supply:
+    description:
+      the regulator that provides 3.3V core power to the hub.
+
+required:
+  - compatible
+  - reg
+
+additionalProperties: false
+
+examples:
+  - |
+    #include <dt-bindings/gpio/gpio.h>
+    usb {
+        dr_mode = "host";
+        #address-cells = <1>;
+        #size-cells = <0>;
+
+        hub: hub@1 {
+            compatible = "usb5e3,608";
+            reg = <1>;
+            reset-gpios = <&pio 7 2 GPIO_ACTIVE_LOW>;
+        };
+    };