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: NThomas Petazzoni <thomas.petazzoni@free-electrons.com>
Acked-by: NAlan Stern <stern@rowland.harvard.edu>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

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

@@ -6,6 +6,11 @@ Required properties:
   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 {