Exynos USB EHCI controllers

Required properties:
  - compatible : should be "samsung,exynos-ehci".
  - reg : should contain at least address and length of the standard EHCI
    register set for the device.
  - interrupts : one EHCI interrupt should be described here.

Optional properties:
  - samsung,vbus-gpio : OF gpio specification of the pin which needs to be
    activated for the bus to be powered.
  - samsung,port_used_bitmap : defined which port should be enabled on the
    root hub.

Example:
	ehci {
		compatible = "samsung,exynos-ehci";
		reg = <0x12110000 0x100>;
		interrupts = <0 71 0>;
		samsung,vbus-gpio = <&gpx1 1 1 3 3>;
		samsung,port_used_bitmap = <0x2>;
	};
