Documentation: DT: dma: Add Xilinx zynqmp dma device tree binding documentation

Xilinx ZynqMP DMA engine, it does support memory to memory transfers,

memory to device and device to memory transfers. It also has flow

control and rate control support for slave/peripheral dma access.

Required properties:

- compatible		: Should be "xlnx,zynqmp-dma-1.0"

- reg			: Memory map for gdma/adma module access.

- interrupt-parent	: Interrupt controller the interrupt is routed through

- interrupts		: Should contain DMA channel interrupt.

- xlnx,bus-width	: Axi buswidth in bits. Should contain 128 or 64

- clock-names		: List of input clocks "clk_main", "clk_apb"

			  (see clock bindings for details)

Optional properties:

- dma-coherent		: Present if dma operations are coherent.

Example:

++++++++

fpd_dma_chan1: dma@fd500000 {

	compatible = "xlnx,zynqmp-dma-1.0";

	reg = <0x0 0xFD500000 0x1000>;

	interrupt-parent = <&gic>;

	interrupts = <0 117 4>;

	clock-names = "clk_main", "clk_apb";

	xlnx,bus-width = <128>;

	dma-coherent;

};