dt-bindings: phy: Add support for QUSB2 phy

Qualcomm QUSB2 phy controller

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QUSB2 controller supports LS/FS/HS usb connectivity on Qualcomm chipsets.

Required properties:

 - compatible: compatible list, contains "qcom,msm8996-qusb2-phy".

 - reg: offset and length of the PHY register set.

 - #phy-cells: must be 0.

 - clocks: a list of phandles and clock-specifier pairs,

	   one for each entry in clock-names.

 - clock-names: must be "cfg_ahb" for phy config clock,

			"ref" for 19.2 MHz ref clk,

			"iface" for phy interface clock (Optional).

 - vdda-pll-supply: Phandle to 1.8V regulator supply to PHY refclk pll block.

 - vdda-phy-dpdm-supply: Phandle to 3.1V regulator supply to Dp/Dm port signals.

 - resets: Phandle to reset to phy block.

Optional properties:

 - nvmem-cells: Phandle to nvmem cell that contains 'HS Tx trim'

		tuning parameter value for qusb2 phy.

 - qcom,tcsr-syscon: Phandle to TCSR syscon register region.

Example:

	hsusb_phy: phy@7411000 {

		compatible = "qcom,msm8996-qusb2-phy";

		reg = <0x7411000 0x180>;

		#phy-cells = <0>;

		clocks = <&gcc GCC_USB_PHY_CFG_AHB2PHY_CLK>,

			<&gcc GCC_RX1_USB2_CLKREF_CLK>,

		clock-names = "cfg_ahb", "ref";

		vdda-pll-supply = <&pm8994_l12>;

		vdda-phy-dpdm-supply = <&pm8994_l24>;

		resets = <&gcc GCC_QUSB2PHY_PRIM_BCR>;

		nvmem-cells = <&qusb2p_hstx_trim>;

        };