The device node for Mediatek USB3 DRD controller

Required properties:
 - compatible : should be "mediatek,<soc-model>-mtu3", "mediatek,mtu3",
	soc-model is the name of SoC, such as mt8512 etc,
	when using "mediatek,mtu3" compatible string, you need SoC specific
	ones in addition, one of:
	- "mediatek,mt8512-mtu3"
 - reg : specifies physical base address and size of the registers
 - reg-names: should be
	- "ippc" : IP Port Control
 - power-domains : a phandle to USB power domain node to control USB's MTCMOS
 - 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", "dma_ck" and "xhci_ck";
 - phys : list of all the USB PHYs on this HCD
 - #address-cells, #size-cells : used for sub-nodes with 'reg' property
 - ranges : allows valid 1:1 translation between child's address space and
	parent's address space

Optional properties:
 - vusb33-supply : regulator of USB AVDD3.3v
 - vbus-supply : regulator of VBUS 5v, needed when supports host mode.

Sub-nodes:
Required properties:
 - compatible : should be "mediatek,ssusb"
 - reg : specifies physical base address and size of the registers
 - reg-names: should be
	- "mac" : SSUSB MAC, include xHCI and device
 - interrupts : interrupt used by xHCI or device
 - dr_mode : should be one of "host" or "peripheral",
	see : usb/generic.txt

Optional properties:
 - pinctrl-names : a pinctrl state named "default" is optional
 - pinctrl-0 : pin control group
	See: pinctrl/pinctrl-bindings.txt

 - device mode:
   - maximum-speed : valid arguments are "full-speed", "high-speed",
	"super-speed" and "super-speed-plus",
	see: usb/generic.txt
   - mediatek,force-vbus : force vbus as valid by SW

 - host mode (dr_mode is "host"):
   - mediatek,u3p-dis-msk : mask to disable u3ports, bit0 for u3port0,
	bit1 for u3port1, ... etc;

Example:
usb3: usb@11213e00 {
	compatible = "mediatek,mt8512-mtu3", "mediatek,mtu3";
	reg = <0x11213e00 0x0100>;
	reg-names = "ippc";
	phys = <&u2port0 PHY_TYPE_USB2>, <&u2port1 PHY_TYPE_USB2>;
	power-domains = <&scpsys MT8512_POWER_DOMAIN_USB>;
	clocks = <&infracfg CLK_INFRA_USB_SYS>,
		 <&topckgen CLK_TOP_SSUSB_TOP_CK_EN>,
		 <&infracfg CLK_INFRA_ICUSB>;
	clock-names = "sys_ck", "ref_ck", "mcu_ck";
	vusb33-supply = <reg_3p3v>;
	vbus-supply = <&usb_p0_vbus>;
	#address-cells = <1>;
	#size-cells = <1>;
	ranges;
	status = "disabled";

	ssusb: usb@11210000 {
		compatible = "mediatek,ssusb";
		reg = <0x11210000 0x3e00>;
		interrupts = <GIC_SPI 16 IRQ_TYPE_LEVEL_LOW>;
		reg-names = "mac";
		dr_mode = "peripheral";
		maximum-speed = "high-speed";
		status = "disabled";
	};
};