Documentation: dt-bindings: update ehci-orion binding documentation

This commit updates the Device Tree binding documentation of
ehci-orion to take into account the fact that we can now optionally
pass a clock and a PHY reference.

Signed-off-by: Thomas Petazzoni <[e-mail]>
Acked-by: Alan Stern <[e-mail]>
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

Documentation/devicetree/bindings/usb/ehci-orion.txt

···
   region.
 - interrupts: The EHCI interrupt
 
+Optional properties:
+- clocks: reference to the clock
+- phys: reference to the USB PHY
+- phy-names: name of the USB PHY, should be "usb"
+
 Example:
 
 	ehci@50000 {