Documentation: DT: vdma: update binding doc for AXI CDMA

This patch updates the device-tree binding doc for
adding support for AXI CDMA.

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>

Documentation/devicetree/bindings/dma/xilinx/xilinx_vdma.txt

@@ -8,8 +8,12 @@ target devices. It can be configured to have one channel or two channels.
 If configured as two channels, one is to transmit to the device and another
 is to receive from the device.
 
+Xilinx AXI CDMA engine, it does transfers between memory-mapped source
+address and a memory-mapped destination address.
+
 Required properties:
-- compatible: Should be "xlnx,axi-vdma-1.00.a" or "xlnx,axi-dma-1.00.a"
+- compatible: Should be "xlnx,axi-vdma-1.00.a" or "xlnx,axi-dma-1.00.a" or
+	      "xlnx,axi-cdma-1.00.a""
 - #dma-cells: Should be <1>, see "dmas" property below
 - reg: Should contain VDMA registers location and length.
 - xlnx,addrwidth: Should be the vdma addressing size in bits(ex: 32 bits).