dt-bindings: Add bindings for USB3 phy on Allwinner H6

The new Allwinner H6 SoC contains a USB3 PHY that is wired to the
external USB3 pins of the SoC.

Add a device tree binding for the PHY.
Signed-off-by: Ondrej Jirman <megous@megous.com>
Acked-by: Maxime Ripard <mripard@kernel.org>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>

Documentation/devicetree/bindings/phy/allwinner,sun50i-h6-usb3-phy.yaml

+# SPDX-License-Identifier: (GPL-2.0 OR BSD-2-Clause)
+# Copyright 2019 Ondrej Jirman <megous@megous.com>
+%YAML 1.2
+---
+$id: "http://devicetree.org/schemas/phy/allwinner,sun50i-h6-usb3-phy.yaml#"
+$schema: "http://devicetree.org/meta-schemas/core.yaml#"
+
+title: Allwinner H6 USB3 PHY
+
+maintainers:
+  - Ondrej Jirman <megous@megous.com>
+
+properties:
+  compatible:
+    enum:
+      - allwinner,sun50i-h6-usb3-phy
+
+  reg:
+    maxItems: 1
+
+  clocks:
+    maxItems: 1
+
+  resets:
+    maxItems: 1
+
+  "#phy-cells":
+    const: 0
+
+required:
+  - compatible
+  - reg
+  - clocks
+  - resets
+  - "#phy-cells"
+
+examples:
+  - |
+    #include <dt-bindings/clock/sun50i-h6-ccu.h>
+    #include <dt-bindings/reset/sun50i-h6-ccu.h>
+    phy@5210000 {
+          compatible = "allwinner,sun50i-h6-usb3-phy";
+          reg = <0x5210000 0x10000>;
+          clocks = <&ccu CLK_USB_PHY1>;
+          resets = <&ccu RST_USB_PHY1>;
+          #phy-cells = <0>;
+    };