dmaengine: xilinx: Use different channel names for each dma

Current driver assumes that child node channel name is either
"xlnx,axi-vdma-mm2s-channel" or "xlnx,axi-vdma-s2mm-channel"
which is confusing the users of AXI DMA and CDMA.
This patch fixes this issue by using different channel
names for the AXI DMA and AXI CDMA child nodes.

Signed-off-by: Kedareswara rao Appana <appanad@xilinx.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>