dmaengine: vdma: Add support for mulit-channel dma mode

This patch adds support for AXI DMA multi-channel dma mode
Multichannel mode enables DMA to connect to multiple masters
and slaves on the streaming side.

In Multichannel mode AXI DMA supports 2D transfers.
Signed-off-by: Kedareswara rao Appana <appanad@xilinx.com>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>