dt-bindings: usb: keystone-usb: Add ti,am654-dwc3 support

The AM654 SoC from TI contains a DWC3 controller. Add
support for it.
Reviewed-by: NRob Herring <robh@kernel.org>
Signed-off-by: NRoger Quadros <rogerq@ti.com>
Signed-off-by: NFelipe Balbi <felipe.balbi@linux.intel.com>

Documentation/devicetree/bindings/usb/keystone-usb.txt

@@ -3,7 +3,9 @@ TI Keystone Soc USB Controller
 DWC3 GLUE
 
 Required properties:
- - compatible: should be "ti,keystone-dwc3".
+ - compatible: should be
+		"ti,keystone-dwc3" for Keystone 2 SoCs
+		"ti,am654-dwc3" for AM654 SoC
  - #address-cells, #size-cells : should be '1' if the device has sub-nodes
    with 'reg' property.
  - reg : Address and length of the register set for the USB subsystem on
@@ -21,7 +23,7 @@ SoCs only:
 - clock-names:		Must be "usb".
 
 
-The following are mandatory properties for Keystone 2 66AK2G SoCs only:
+The following are mandatory properties for 66AK2G and AM654:
 
 - power-domains:	Should contain a phandle to a PM domain provider node
 			and an args specifier containing the USB device id