dt-bindings: Add usb3.0 phy binding for MT65xx SoCs

mt65xx USB3.0 PHY binding

--------------------------

This binding describes a usb3.0 phy for mt65xx platforms of Medaitek SoC.

Required properties (controller (parent) node):

 - compatible	: should be "mediatek,mt8173-u3phy"

 - reg		: offset and length of register for phy, exclude port's

		  register.

 - clocks	: a list of phandle + clock-specifier pairs, one for each

		  entry in clock-names

 - clock-names	: must contain

		  "u3phya_ref": for reference clock of usb3.0 analog phy.

Required nodes	: a sub-node is required for each port the controller

		  provides. Address range information including the usual

		  'reg' property is used inside these nodes to describe

		  the controller's topology.

Required properties (port (child) node):

- reg		: address and length of the register set for the port.

- #phy-cells	: should be 1 (See second example)

		  cell after port phandle is phy type from:

			- PHY_TYPE_USB2

			- PHY_TYPE_USB3

Example:

u3phy: usb-phy@11290000 {

	compatible = "mediatek,mt8173-u3phy";

	reg = <0 0x11290000 0 0x800>;

	clocks = <&apmixedsys CLK_APMIXED_REF2USB_TX>;

	clock-names = "u3phya_ref";

	#address-cells = <2>;

	#size-cells = <2>;

	ranges;

	status = "okay";

	phy_port0: port@11290800 {

		reg = <0 0x11290800 0 0x800>;

		#phy-cells = <1>;

		status = "okay";

	};

	phy_port1: port@11291000 {

		reg = <0 0x11291000 0 0x800>;

		#phy-cells = <1>;

		status = "okay";

	};

};

Specifying phy control of devices

---------------------------------

Device nodes should specify the configuration required in their "phys"

property, containing a phandle to the phy port node and a device type;

phy-names for each port are optional.

Example:

#include <dt-bindings/phy/phy.h>

usb30: usb@11270000 {

	...

	phys = <&phy_port0 PHY_TYPE_USB3>;

	phy-names = "usb3-0";

	...

};