dt-bindings: usb: ti,keystone-dwc3.yaml: Add USB3.0 PHY property

AM654 SoC requires USB3.0 PHY to be turned on before the USB controller.
For this SoC, the 'phys' property is used to provide the USB3.0
reference.
Signed-off-by: Roger Quadros <rogerq@ti.com>
Signed-off-by: Felipe Balbi <balbi@kernel.org>

Documentation/devicetree/bindings/usb/ti,keystone-dwc3.yaml

@@ -34,6 +34,16 @@ properties:
       value. This property is as per the binding,
       Documentation/devicetree/bindings/soc/ti/sci-pm-domain.txt
 
+  phys:
+    description:
+      PHY specifier for the USB3.0 PHY. Some SoCs need the USB3.0 PHY
+      to be turned on before the controller.
+      Documentation/devicetree/bindings/phy/phy-bindings.txt
+
+  phy-names:
+    items:
+      - const: "usb3-phy"
+
   dwc3:
     description: This is the node representing the DWC3 controller instance
       Documentation/devicetree/bindings/usb/dwc3.txt