ST USB EHCI controller

Required properties:
 - compatible		: must be "st,st-ehci-300x"
 - reg			: physical base addresses of the controller and length of memory mapped
			  region
 - interrupts		: one EHCI interrupt should be described here
 - pinctrl-names	: a pinctrl state named "default" must be defined
 - pinctrl-0		: phandle referencing pin configuration of the USB controller
See: Documentation/devicetree/bindings/pinctrl/pinctrl-bindings.txt
 - clocks		: phandle list of usb clocks
 - clock-names		: should be "ic" for interconnect clock and "clk48"
See: Documentation/devicetree/bindings/clock/clock-bindings.txt

 - phys			: phandle for the PHY device
 - phy-names		: should be "usb"
 - resets		: phandle + reset specifier pairs to the powerdown and softreset lines
			  of the USB IP
 - reset-names		: should be "power" and "softreset"
See: Documentation/devicetree/bindings/reset/st,sti-powerdown.txt
See: Documentation/devicetree/bindings/reset/reset.txt

Example:

	ehci1: usb@0xfe203e00 {
		compatible = "st,st-ehci-300x";
		reg = <0xfe203e00 0x100>;
		interrupts = <GIC_SPI 148 IRQ_TYPE_NONE>;
		pinctrl-names = "default";
		pinctrl-0 = <&pinctrl_usb1>;
		clocks = <&clk_s_a1_ls 0>;
		phys = <&usb2_phy>;
		phy-names = "usb";
		status = "okay";

		resets = <&powerdown STIH416_USB1_POWERDOWN>,
			 <&softreset STIH416_USB1_SOFTRESET>;
		reset-names = "power", "softreset";
	};
