dt-bindings: usb: Add binding for Realtek RTS5411 hub controller

The Realtek RTS5411 is a USB 3.0 hub controller with 4 ports.

This initial version of the binding only describes USB related
aspects of the RTS5411, it does not cover the option of
connecting the controller as an i2c slave.

Reviewed-by: Rob Herring <[e-mail]>
Signed-off-by: Matthias Kaehlcke <[e-mail]>
Link: https://lore.kernel.org/r/20210609150159.v12.1.I248292623d3d0f6a4f0c5bc58478ca3c0062b49a@changeid
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

Documentation/devicetree/bindings/usb/realtek,rts5411.yaml

···
+# SPDX-License-Identifier: GPL-2.0-only or BSD-2-Clause
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/usb/realtek,rts5411.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Binding for the Realtek RTS5411 USB 3.0 hub controller
+
+maintainers:
+  - Matthias Kaehlcke <[e-mail]>
+
+allOf:
+  - $ref: usb-device.yaml#
+
+properties:
+  compatible:
+    items:
+      - enum:
+          - usbbda,5411
+          - usbbda,411
+
+  reg: true
+
+  vdd-supply:
+    description:
+      phandle to the regulator that provides power to the hub.
+
+  companion-hub:
+    $ref: '/schemas/types.yaml#/definitions/phandle'
+    description:
+      phandle to the companion hub on the controller.
+
+required:
+  - companion-hub
+  - compatible
+  - reg
+
+additionalProperties: false
+
+examples:
+  - |
+    usb {
+        dr_mode = "host";
+        #address-cells = <1>;
+        #size-cells = <0>;
+
+        /* 2.0 hub on port 1 */
+        hub_2_0: hub@1 {
+            compatible = "usbbda,5411";
+            reg = <1>;
+            vdd-supply = <&pp3300_hub>;
+            companion-hub = <&hub_3_0>;
+        };
+
+        /* 3.0 hub on port 2 */
+        hub_3_0: hub@2 {
+            compatible = "usbbda,411";
+            reg = <2>;
+            vdd-supply = <&pp3300_hub>;
+            companion-hub = <&hub_2_0>;
+        };
+    };