dt-bindings: Add Broadcom STB USB PHY binding document

Broadcom STB USB PHY

Required properties:

 - compatible: brcm,brcmstb-usb-phy

 - reg: two offset and length pairs.

	The first pair specifies a manditory set of memory mapped

	registers used for general control of the PHY.

	The second pair specifies optional registers used by some of

	the SoCs that support USB 3.x

 - #phy-cells: Shall be 1 as it expects one argument for setting

	       the type of the PHY. Possible values are:

	       - PHY_TYPE_USB2 for USB1.1/2.0 PHY

	       - PHY_TYPE_USB3 for USB3.x PHY

Optional Properties:

- clocks : clock phandles.

- clock-names: String, clock name.

- brcm,ipp: Boolean, Invert Port Power.

  Possible values are: 0 (Don't invert), 1 (Invert)

- brcm,ioc: Boolean, Invert Over Current detection.

  Possible values are: 0 (Don't invert), 1 (Invert)

NOTE: one or both of the following two properties must be set

- brcm,has-xhci: Boolean indicating the phy has an XHCI phy.

- brcm,has-eohci: Boolean indicating the phy has an EHCI/OHCI phy.

- dr_mode: String, PHY Device mode.

  Possible values are: "host", "peripheral ", "drd" or "typec-pd"

  If this property is not defined, the phy will default to "host" mode.

Example:

usbphy_0: usb-phy@f0470200 {

	reg = <0xf0470200 0xb8>,

		<0xf0471940 0x6c0>;

	compatible = "brcm,brcmstb-usb-phy";

	#phy-cells = <1>;

	dr_mode = "host"

	brcm,ioc = <1>;

	brcm,ipp = <1>;

	brcm,has-xhci;

	brcm,has-eohci;

	clocks = <&usb20>, <&usb30>;

	clock-names = "sw_usb", "sw_usb3";

};