dt-binding: usb: xilinx: Add clocking node

Add a clocking node for xilinx udc.
Signed-off-by: Shubhrajyoti Datta <shubhrajyoti.datta@xilinx.com>
Signed-off-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/30c7d87ab46a0ea2da2dd04d824f162a2e3da4c8.1632805672.git.shubhrajyoti.datta@xilinx.com

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

@@ -24,6 +24,12 @@ properties:
       If present, hardware has dma capability.
     type: boolean
 
+  clocks:
+    minItems: 1
+
+  clock-names:
+    const: s_axi_aclk
+
 required:
   - compatible
   - reg