dt-bindings: phy: mxs-usb-phy: Add i.MX8DXL compatible string

Add compatible for i.MX8DXL USB PHY.
Signed-off-by: Abel Vesa <abel.vesa@nxp.com>
Acked-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20220607111625.1845393-9-abel.vesa@nxp.comSigned-off-by: Vinod Koul <vkoul@kernel.org>

Documentation/devicetree/bindings/phy/mxs-usb-phy.txt

@@ -8,6 +8,7 @@ Required properties:
 	* "fsl,vf610-usbphy" for Vybrid vf610
 	* "fsl,imx6sx-usbphy" for imx6sx
 	* "fsl,imx7ulp-usbphy" for imx7ulp
+	* "fsl,imx8dxl-usbphy" for imx8dxl
   "fsl,imx23-usbphy" is still a fallback for other strings
 - reg: Should contain registers location and length
 - interrupts: Should contain phy interrupt