usb: dwc3: of-simple: add compatible for Cavium

Add necessary compatible flag for Cavium's DWC3 so
dwc3-of-simple will probe.
Tested-by: Steven J. Hill <Steven.Hill@cavium.com>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>

Documentation/devicetree/bindings/usb/dwc3-cavium.txt

+Cavium SuperSpeed DWC3 USB SoC controller
+
+Required properties:
+- compatible:	Should contain "cavium,octeon-7130-usb-uctl"
+
+Required child node:
+A child node must exist to represent the core DWC3 IP block. The name of
+the node is not important. The content of the node is defined in dwc3.txt.
+
+Example device node:
+
+		    uctl@1180069000000 {
+			    compatible = "cavium,octeon-7130-usb-uctl";
+			    reg = <0x00011800 0x69000000 0x00000000 0x00000100>;
+			    ranges;
+			    #address-cells = <0x00000002>;
+			    #size-cells = <0x00000002>;
+			    refclk-frequency = <0x05f5e100>;
+			    refclk-type-ss = "dlmc_ref_clk0";
+			    refclk-type-hs = "dlmc_ref_clk0";
+			    power = <0x00000002 0x00000002 0x00000001>;
+			    xhci@1690000000000 {
+				    compatible = "cavium,octeon-7130-xhci", "synopsys,dwc3";
+				    reg = <0x00016900 0x00000000 0x00000010 0x00000000>;
+				    interrupt-parent = <0x00000010>;
+				    interrupts = <0x00000009 0x00000004>;
+			    };
+		    };

drivers/usb/dwc3/dwc3-of-simple.c

@@ -176,6 +176,7 @@ static const struct of_device_id of_dwc3_simple_match[] = {
 	{ .compatible = "qcom,dwc3" },
 	{ .compatible = "rockchip,rk3399-dwc3" },
 	{ .compatible = "xlnx,zynqmp-dwc3" },
+	{ .compatible = "cavium,octeon-7130-usb-uctl" },
 	{ /* Sentinel */ }
 };
 MODULE_DEVICE_TABLE(of, of_dwc3_simple_match);