Enable support for Xilinx AXI VDMA Soft IP.

AXI VDMA engine provides high-bandwidth direct memory access
between memory and AXI4-Stream video type target
peripherals including peripherals which support AXI4-
Stream Video Protocol. It has two stream interfaces/
channels, Memory Mapped to Stream (MM2S) and Stream to
Memory Mapped (S2MM) for the data transfers.
AXI CDMA engine provides high-bandwidth direct memory access
between a memory-mapped source address and a memory-mapped
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.

source code:

drivers/dma/xilinx/xilinx_dma.c