dt-bindings: usb: renesas_usb3: Document usb role switch support

Update the DT bindings documentation to support usb role switch
for USB Type-C connector using USB role switch class framework.
Signed-off-by: Biju Das <biju.das@bp.renesas.com>
Reviewed-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/1567584941-13690-4-git-send-email-biju.das@bp.renesas.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Documentation/devicetree/bindings/usb/renesas,usb3-peri.txt

@@ -22,6 +22,12 @@ Required properties:
 Optional properties:
   - phys: phandle + phy specifier pair
   - phy-names: must be "usb"
+  - usb-role-switch: support role switch. see usb/generic.txt
+
+Sub-nodes:
+- any connector to the data bus of this controller should be modelled using the
+  OF graph bindings specified in bindings/graph.txt, if the "usb-role-switch"
+  property is used.
 
 Example of R-Car H3 ES1.x:
 	usb3_peri0: usb@ee020000 {
@@ -39,3 +45,20 @@ Example of R-Car H3 ES1.x:
 		interrupts = <GIC_SPI 100 IRQ_TYPE_LEVEL_HIGH>;
 		clocks = <&cpg CPG_MOD 327>;
 	};
+
+Example of RZ/G2E:
+	usb3_peri0: usb@ee020000 {
+		compatible = "renesas,r8a774c0-usb3-peri",
+			     "renesas,rcar-gen3-usb3-peri";
+		reg = <0 0xee020000 0 0x400>;
+		interrupts = <GIC_SPI 104 IRQ_TYPE_LEVEL_HIGH>;
+		clocks = <&cpg CPG_MOD 328>;
+		companion = <&xhci0>;
+		usb-role-switch;
+
+		port {
+			usb3_role_switch: endpoint {
+				remote-endpoint = <&hd3ss3220_ep>;
+			};
+		};
+	};