dt-bindings: phy: mxs-usb-phy: add imx8qxp compatible

Add "fsl,imx8qxp-usbphy" compatible.

Signed-off-by: Xu Yang <[e-mail]>
Acked-by: Conor Dooley <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Vinod Koul <[e-mail]>

Documentation/devicetree/bindings/phy/fsl,mxs-usbphy.yaml

···
           - enum:
               - fsl,imx8dxl-usbphy
               - fsl,imx8qm-usbphy
+              - fsl,imx8qxp-usbphy
               - fsl,imx8ulp-usbphy
           - const: fsl,imx7ulp-usbphy