dt-bindings: usb: dwc3-xilinx: allow dma-coherent

On Versal Gen 2 SoC the LPD USB DMA controller is coherent with the CPU
so allow specifying the information.

Signed-off-by: Radhey Shyam Pandey <radhey.shyam.pandey@amd.com>
Link: https://lore.kernel.org/r/1747401516-286356-1-git-send-email-radhey.shyam.pandey@amd.com


Signed-off-by: Rob Herring (Arm) <robh@kernel.org>