dt-bindings: phy: ti: Add support for AM654x USB2 PHY

Add support for USB2 PHY on AM654x SoC.
Signed-off-by: Roger Quadros <rogerq@ti.com>
Signed-off-by: Sekhar Nori <nsekhar@ti.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>

Documentation/devicetree/bindings/phy/ti-phy.txt

@@ -35,6 +35,7 @@ Required properties:
 	       DRA7x
 	       Should be "ti,dra7x-usb2-phy2" for the 2nd instance of USB2 PHY
 	       in DRA7x
+	       Should be "ti,am654-usb2" for the USB2 PHYs on AM654.
  - reg : Address and length of the register set for the device.
  - #phy-cells: determine the number of cells that should be given in the
    phandle while referencing this phy.