The device node for Mediatek USB3.0 DRD controller

Required properties:
 - compatible : should be "mediatek,<soc-model>-mtu3", "mediatek,mtu3",
	soc-model is the name of SoC, such as mt8173, mt2712 etc,
	when using "mediatek,mtu3" compatible string, you need SoC specific
	ones in addition, one of:
	- "mediatek,mt8173-mtu3"
 - reg : specifies physical base address and size of the registers
 - reg-names: should be "mac" for device IP and "ippc" for IP port control
 - interrupts : interrupt used by the device IP
 - power-domains : a phandle to USB power domain node to control USB's
	mtcmos
 - vusb33-supply : regulator of USB avdd3.3v
 - clocks : a list of phandle + clock-specifier pairs, one for each
	entry in clock-names
 - clock-names : must contain "sys_ck" for clock of controller,
	the following clocks are optional:
	"ref_ck", "mcu_ck" and "dam_ck";
 - phys : a list of phandle + phy specifier pairs
 - dr_mode : should be one of "host", "peripheral" or "otg",
	refer to usb/generic.txt

Optional properties:
 - #address-cells, #size-cells : should be '2' if the device has sub-nodes
	with 'reg' property
 - ranges : allows valid 1:1 translation between child's address space and
	parent's address space
 - extcon : external connector for vbus and idpin changes detection, needed
	when supports dual-role mode.
 - vbus-supply : reference to the VBUS regulator, needed when supports
	dual-role mode.
 - pinctrl-names : a pinctrl state named "default" is optional, and need be
	defined if auto drd switch is enabled, that means the property dr_mode
	is set as "otg", and meanwhile the property "mediatek,enable-manual-drd"
	is not set.
 - pinctrl-0 : pin control group
	See: Documentation/devicetree/bindings/pinctrl/pinctrl-bindings.txt

 - maximum-speed : valid arguments are "super-speed", "high-speed" and
	"full-speed"; refer to usb/generic.txt
 - enable-manual-drd : supports manual dual-role switch via debugfs; usually
	used when receptacle is TYPE-A and also wants to support dual-role
	mode.
 - mediatek,enable-wakeup : supports ip sleep wakeup used by host mode
 - mediatek,syscon-wakeup : phandle to syscon used to access USB wakeup
	control register, it depends on "mediatek,enable-wakeup".
 - mediatek,u3p-dis-msk : mask to disable u3ports, bit0 for u3port0,
	bit1 for u3port1, ... etc;

Sub-nodes:
The xhci should be added as subnode to mtu3 as shown in the following example
if host mode is enabled. The DT binding details of xhci can be found in:
Documentation/devicetree/bindings/usb/mediatek,mtk-xhci.txt

Example:
ssusb: usb@11271000 {
	compatible = "mediatek,mt8173-mtu3";
	reg = <0 0x11271000 0 0x3000>,
	      <0 0x11280700 0 0x0100>;
	reg-names = "mac", "ippc";
	interrupts = <GIC_SPI 64 IRQ_TYPE_LEVEL_LOW>;
	phys = <&phy_port0 PHY_TYPE_USB3>,
	       <&phy_port1 PHY_TYPE_USB2>;
	power-domains = <&scpsys MT8173_POWER_DOMAIN_USB>;
	clocks = <&topckgen CLK_TOP_USB30_SEL>, <&clk26m>,
		 <&pericfg CLK_PERI_USB0>,
		 <&pericfg CLK_PERI_USB1>;
	clock-names = "sys_ck", "ref_ck";
	vusb33-supply = <&mt6397_vusb_reg>;
	vbus-supply = <&usb_p0_vbus>;
	extcon = <&extcon_usb>;
	dr_mode = "otg";
	mediatek,enable-wakeup;
	mediatek,syscon-wakeup = <&pericfg>;
	#address-cells = <2>;
	#size-cells = <2>;
	ranges;

	usb_host: xhci@11270000 {
		compatible = "mediatek,mt8173-xhci";
		reg = <0 0x11270000 0 0x1000>;
		reg-names = "mac";
		interrupts = <GIC_SPI 115 IRQ_TYPE_LEVEL_LOW>;
		power-domains = <&scpsys MT8173_POWER_DOMAIN_USB>;
		clocks = <&topckgen CLK_TOP_USB30_SEL>, <&clk26m>;
		clock-names = "sys_ck", "ref_ck";
		vusb33-supply = <&mt6397_vusb_reg>;
	};
};