dt-binding: usb: xilinx: Convert binding to YAML

Convert the current udc xilinx binding from text format to YAML
format/DT schema, and delete the legacy text binding file.

Signed-off-by: Shubhrajyoti Datta <shubhrajyoti.datta@xilinx.com>
Link: https://lore.kernel.org/r/20210826053433.1599019-1-shubhrajyoti.datta@xilinx.com
Signed-off-by: Rob Herring <robh@kernel.org>