dmaengine: xilinx_dma: Remove axidma multichannel mode 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. So inline with it remove axidma multichannel support from
from the driver.

Signed-off-by: Radhey Shyam Pandey <radhey.shyam.pandey@xilinx.com>
Link: https://lore.kernel.org/r/1571763622-29281-5-git-send-email-radhey.shyam.pandey@xilinx.com


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