* USB (Universal Serial Bus Controller)

Required properties:
- compatible : could be "qe_udc" or "fhci-hcd".
- mode : the could be "host" or "slave".
- reg : Offset and length of the register set for the device
- interrupts : <a b> where a is the interrupt number and b is a
  field that represents an encoding of the sense and level
  information for the interrupt.  This should be encoded based on
  the information in section 2) depending on the type of interrupt
  controller you have.
- interrupt-parent : the phandle for the interrupt controller that
  services interrupts for this device.

Example(slave):
	usb@6c0 {
		compatible = "qe_udc";
		reg = <6c0 40>;
		interrupts = <8b 0>;
		interrupt-parent = <700>;
		mode = "slave";
	};