dmaengine: xilinx_dma: Add Xilinx AXI MCDMA Engine driver support

dmaengine: xilinx_dma: Add Xilinx AXI MCDMA Engine driver support

Add support for AXI Multichannel Direct Memory Access (AXI MCDMA)
core, which is a soft Xilinx IP core that provides high-bandwidth
direct memory access between memory and AXI4-Stream target peripherals.
The AXI MCDMA core provides scatter-gather interface with multiple
independent transmit and receive channels. The driver supports
device_prep_slave_sg slave transfer mode.

Signed-off-by: Radhey Shyam Pandey <radhey.shyam.pandey@xilinx.com>
Link: https://lore.kernel.org/r/1571763622-29281-7-git-send-email-radhey.shyam.pandey@xilinx.com
Signed-off-by: Vinod Koul <vkoul@kernel.org>