dt-bindings: phy: Add support for QUSB2 phy

Qualcomm chipsets have QUSB2 phy controller that provides
HighSpeed functionality for DWC3 controller.
Adding dt binding information for the same.
Signed-off-by: Vivek Gautam <vivek.gautam@codeaurora.org>
Reviewed-by: Stephen Boyd <sboyd@codeaurora.org>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>

Documentation/devicetree/bindings/phy/qcom-qusb2-phy.txt

+Qualcomm QUSB2 phy controller
+=============================
+
+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>;
+        };