* Freescale i.MX8MQ USB3 PHY binding

Required properties:
- compatible:	Should be "fsl,imx8mq-usb-phy" or "fsl,imx8mp-usb-phy"
- #phys-cells:	must be 0 (see phy-bindings.txt in this directory)
- reg:		The base address and length of the registers
- clocks:	phandles to the clocks for each clock listed in clock-names
- clock-names:	must contain "phy"

Optional properties:
- vbus-supply: A phandle to the regulator for USB VBUS.
- vbus-power-supply: A phandle to the vbus power supply provider, used to
		     to detect the possible BC charger type of it.
- fsl,phy-tx-vref-tune: Adjusts the high-speed DC level voltage.
			- 1111: + 24%
			- 1110: + 22%
			.....
			- 0101: + 4%
			- 0100: + 2%
			- 0011: 0 (default on imx8mp)
			- 0010: – 2%
			- 0001: – 4%
			- 0000: – 6%
- fsl,phy-tx-rise-tune: Adjusts the rise/fall times of the high-speed waveform.
			- 11: – 3%
			- 10: – 1%
			- 01: 0 (default on imx8mp)
			- 00: + 3%
- fsl,phy-tx-preemp-amp-tune: This property controls the amount of current
			    source to DP<#> and DM<#> after a J-to-K or K-to-J
			    transition. The HS Transmitter pre-emphasis current
			    is defined in terms of unit amounts. One unit
			    amount is approximately 600 μA and is defined as 1X
			    pre-emphasis current.
				- 11: 3x pre-emphasis current
				- 10: 2x pre-emphasis current
				- 01: 1x pre-emphasis current
				- 00: Disabled (default on imx8mp)
- fsl,phy-comp-dis-tune: Adjusts the voltage level for the threshold used to
			 detect a disconnect event at the host.
				- 111: + 15.54%
				- 110: + 11.86%
				- 101: + 7.52%
				- 100: + 4.08%
				- 011: 0 (default on imx8mp)
				- 010: – 3.04%
				- 001: – 6.5%
				- 000: – 9.01%
- fsl,pcs-tx-deemph-3p5db: This property sets the TX driver de-emphasis value
			   when pipeP_tx_deemph[1:0] is set to 2’b01 (according
			   to the PIPE3 specification), default value is 23 on
			   imx8mp.
- fsl,phy-pcs-tx-swing-full: This property sets the launch amplitude of the
			     transmitter, default value is 120 (7b'1111000)
			     on imx8mp.
Example:
	usb3_phy0: phy@381f0040 {
		compatible = "fsl,imx8mq-usb-phy";
		reg = <0x381f0040 0x40>;
		clocks = <&clk IMX8MQ_CLK_USB1_PHY_ROOT>;
		clock-names = "phy";
		#phy-cells = <0>;
	};