ST DWC3 glue logic

This file documents the parameters for the dwc3-st driver
This driver provides the glue logic to use the dwc3 on STiH407 platforms based.

Required properties:
 - compatible: must be "st,stih407-dwc3"
 - reg		: glue logic base address and USB syscfg ctrl register offest
 - reg-names	: register names.
 - st,syscon    : should be phandle to system configuration node which
		  encompases this glue registers.
 - resets       : phandle pointing to the system reset controller
 - #address-cells : must be <1>
 - pinctrl-0	: Pin control group

Optional properties:
 - st,dwc3-drd-device: to program the HC as "device" (static setup)
 - st,gsbuscfg: to set the gsbuscfg dwc3 core registers with different values
		than default. Requested by stih410 and stih418 at the moment.
		The property needs two values for the two bus registers, so
		st,gsbuscfg = <#0 #1>;

The DWC3 is a subnode to DWC3 core driver as shown below.
Take a look at Documentation/devicetree/bindings/usb/dwc3.txt

Example:

st_dwc3: dwc3@8f94000 {
	status		= "disabled";
	compatible	= "st,stih407-dwc3";
	reg		= <0x08f94000 0x1000>, <0x110 0x4>;
	reg-names	= "reg-glue", "syscfg-reg";
	st,syscfg	= <&syscfg_core>;
	resets          = <&powerdown STIH407_USB3_POWERDOWN>;
	#address-cells	= <1>;
	#size-cells	= <1>;
	pinctrl-names	= "default";
	pinctrl-0	= <&pinctrl_usb3>;
	ranges;

	dwc3: dwc3@9900000 {
		compatible	= "synopsys,dwc3";
		reg		= <0x09900000 0x100000>;
		interrupts	=  <GIC_SPI 155 IRQ_TYPE_NONE>;

		/* usb2 picophy port2, MiPHY2 port for USB3 */
		phys = <&usb3_picophy>;
		phy-names = "usb2-phy";

		usb3-phy = <&usb3_phy>;
	};
};
