Xilinx AXI DMA engine, it does transfers between memory and AXI4 stream
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.

Required properties:
- compatible: Should be "xlnx,axi-dma-1.00.a"
- #dma-cells: Should be <1>, see "dmas" property below
- reg: Should contain DMA registers location and length.
- dma-channel child node: Should have at least one channel and can have up to
	two channels per device. This node specifies the properties of each
	DMA channel (see child node properties below).

Optional properties:
- xlnx,include-sg: Tells whether configured for Scatter-mode in
	the hardware.

Required child node properties:
- compatible: It should be either "xlnx,axi-dma-mm2s-channel" or
	"xlnx,axi-dma-s2mm-channel".
- interrupts: Should contain per channel DMA interrupts.
- xlnx,datawidth: Should contain the stream data width, take values
	{32,64...1024}.

Option child node properties:
- xlnx,include-dre: Tells whether hardware is configured for Data
	Realignment Engine.

Example:
++++++++

axi_dma_0: axidma@40400000 {
	compatible = "xlnx,axi-dma-1.00.a";
	#dma_cells = <1>;
	reg = < 0x40400000 0x10000 >;
	dma-channel@40400000 {
		compatible = "xlnx,axi-dma-mm2s-channel";
		interrupts = < 0 59 4 >;
		xlnx,datawidth = <0x40>;
	} ;
	dma-channel@40400030 {
		compatible = "xlnx,axi-dma-s2mm-channel";
		interrupts = < 0 58 4 >;
		xlnx,datawidth = <0x40>;
	} ;
} ;


* DMA client

Required properties:
- dmas: a list of <[DMA device phandle] [Channel ID]> pairs,
	where Channel ID is '0' for write/tx and '1' for read/rx
	channel.
- dma-names: a list of DMA channel names, one per "dmas" entry

Example:
++++++++

dmatest_0: dmatest@0 {
	compatible ="xlnx,axi-dma-test-1.00.a";
	dmas = <&axi_dma_0 0
		&axi_dma_0 1>;
	dma-names = "dma0", "dma1";
} ;