dt-bindings: phy: qcom,qusb2: document ipq6018 compatible

This compatible string is for the USB PHY on IPQ60xx systems.
Signed-off-by: Baruch Siach <baruch@tkos.co.il>
Link: https://lore.kernel.org/r/7e1e7bda6ccdaab9adeeb956fac1acc39908a8dc.1611756920.git.baruch@tkos.co.ilSigned-off-by: Vinod Koul <vkoul@kernel.org>

Documentation/devicetree/bindings/phy/qcom,qusb2-phy.yaml

@@ -22,6 +22,7 @@ properties:
               - qcom,msm8996-qusb2-phy
               - qcom,msm8998-qusb2-phy
               - qcom,sdm660-qusb2-phy
+              - qcom,ipq6018-qusb2-phy
       - items:
           - enum:
               - qcom,sc7180-qusb2-phy