USB xHCI controllers

Required properties:
  - compatible: should be one or more of

    - "generic-xhci" for generic XHCI device
    - "marvell,armada-375-xhci" for Armada 375 SoCs
    - "marvell,armada-380-xhci" for Armada 38x SoCs
    - "renesas,xhci-r8a7790" for r8a7790 SoC
    - "renesas,xhci-r8a7791" for r8a7791 SoC
    - "renesas,xhci-r8a7793" for r8a7793 SoC
    - "renesas,xhci-r8a7795" for r8a7795 SoC
    - "renesas,rcar-gen2-xhci" for a generic R-Car Gen2 compatible device
    - "renesas,rcar-gen3-xhci" for a generic R-Car Gen3 compatible device
    - "xhci-platform" (deprecated)

    When compatible with the generic version, nodes must list the
    SoC-specific version corresponding to the platform first
    followed by the generic version.

  - reg: should contain address and length of the standard XHCI
    register set for the device.
  - interrupts: one XHCI interrupt should be described here.

Optional properties:
  - clocks: reference to a clock
  - usb3-lpm-capable: determines if platform is USB3 LPM capable

Example:
	usb@f0931000 {
		compatible = "generic-xhci";
		reg = <0xf0931000 0x8c8>;
		interrupts = <0x0 0x4e 0x0>;
	};