Documentation: bindings: add DT documentation for Rockchip USB2PHY

Signed-off-by: Frank Wang <frank.wang@rock-chips.com>
Acked-by: Rob Herring <robh@kernel.org>
Reviewed-by: Heiko Stuebner <heiko@sntech.de>
Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>

Documentation/devicetree/bindings/phy/phy-rockchip-inno-usb2.txt

+ROCKCHIP USB2.0 PHY WITH INNO IP BLOCK
+
+Required properties (phy (parent) node):
+ - compatible : should be one of the listed compatibles:
+	* "rockchip,rk3366-usb2phy"
+	* "rockchip,rk3399-usb2phy"
+ - reg : the address offset of grf for usb-phy configuration.
+ - #clock-cells : should be 0.
+ - clock-output-names : specify the 480m output clock name.
+
+Optional properties:
+ - clocks : phandle + phy specifier pair, for the input clock of phy.
+ - clock-names : input clock name of phy, must be "phyclk".
+
+Required nodes : a sub-node is required for each port the phy provides.
+		 The sub-node name is used to identify host or otg port,
+		 and shall be the following entries:
+	* "otg-port" : the name of otg port.
+	* "host-port" : the name of host port.
+
+Required properties (port (child) node):
+ - #phy-cells : must be 0. See ./phy-bindings.txt for details.
+ - interrupts : specify an interrupt for each entry in interrupt-names.
+ - interrupt-names : a list which shall be the following entries:
+	* "otg-id" : for the otg id interrupt.
+	* "otg-bvalid" : for the otg vbus interrupt.
+	* "linestate" : for the host/otg linestate interrupt.
+
+Optional properties:
+ - phy-supply : phandle to a regulator that provides power to VBUS.
+		See ./phy-bindings.txt for details.
+
+Example:
+
+grf: syscon@ff770000 {
+	compatible = "rockchip,rk3366-grf", "syscon", "simple-mfd";
+	#address-cells = <1>;
+	#size-cells = <1>;
+
+...
+
+	u2phy: usb2-phy@700 {
+		compatible = "rockchip,rk3366-usb2phy";
+		reg = <0x700 0x2c>;
+		#clock-cells = <0>;
+		clock-output-names = "sclk_otgphy0_480m";
+
+		u2phy_otg: otg-port {
+			#phy-cells = <0>;
+			interrupts = <GIC_SPI 93 IRQ_TYPE_LEVEL_HIGH>,
+				     <GIC_SPI 94 IRQ_TYPE_LEVEL_HIGH>,
+				     <GIC_SPI 95 IRQ_TYPE_LEVEL_HIGH>;
+			interrupt-names = "otg-id", "otg-bvalid", "linestate";
+			status = "okay";
+		};
+
+		u2phy_host: host-port {
+			#phy-cells = <0>;
+			interrupts = <GIC_SPI 96 IRQ_TYPE_LEVEL_HIGH>;
+			interrupt-names = "linestate";
+			status = "okay";
+		};
+	};
+};