dt-bindings: dmaengine: xilinx_dma: Remove axidma multichannel support

The AXI DMA multichannel support is deprecated in the IP and it is no
longer actively supported. For multichannel support, refer to the AXI
multichannel direct memory access IP product guide(PG228) and MCDMA
driver(added in the subsequent commits). Inline with it remove axidma
multichannel optional properties i.e xlnx,mcdma and dma-channels from
the binding description.

Signed-off-by: Radhey Shyam Pandey <radhey.shyam.pandey@xilinx.com>
Acked-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/1571763622-29281-2-git-send-email-radhey.shyam.pandey@xilinx.com


Signed-off-by: Vinod Koul <vkoul@kernel.org>