ARM: dts: qcom: sdx55: Add support for PCIe PHY

Add devicetree support for PCIe PHY used in SDX55 platform. This PHY is
used by the PCIe EP controller.

Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Link: https://lore.kernel.org/r/20211126070520.28979-2-manivannan.sadhasivam@linaro.org