dt-binding: usb: xilinx: Add clocking node

Add a clocking node for xilinx udc.

Signed-off-by: Shubhrajyoti Datta <[e-mail]>
Signed-off-by: Rob Herring <[e-mail]>
Link: https://lore.kernel.org/r/30c7d87ab4[e-mail]

Documentation/devicetree/bindings/usb/xlnx,usb2.yaml

···
       If present, hardware has dma capability.
     type: boolean
 
+  clocks:
+    minItems: 1
+
+  clock-names:
+    const: s_axi_aclk
+
 required:
   - compatible
   - reg