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>

drivers/dma/Kconfig

@@ -655,6 +655,10 @@ config XILINX_DMA
 	  destination address.
 	  AXI DMA engine provides high-bandwidth one dimensional direct
 	  memory access between memory and AXI4-Stream target peripherals.
+	  AXI MCDMA engine provides high-bandwidth direct memory access
+	  between memory and AXI4-Stream target peripherals. It provides
+	  the scatter gather interface with multiple channels independent
+	  configuration support.
 
 config XILINX_ZYNQMP_DMA
 	tristate "Xilinx ZynqMP DMA Engine"