arm64: dts: msm8996: Add device node for qcom qusb2 phy

Adding device node for QUSB2 phy and the required infrastructure
to enable support for the same. This phy is used by dwc3 controller
present on msm8996.

Signed-off-by: Vivek Gautam <vivek.gautam@codeaurora.org>
Signed-off-by: Andy Gross <andy.gross@linaro.org>