dt-bindings: dmaengine: Add Spreadtrum SC9860 DMA controller

* Spreadtrum DMA controller

This binding follows the generic DMA bindings defined in dma.txt.

Required properties:

- compatible: Should be "sprd,sc9860-dma".

- reg: Should contain DMA registers location and length.

- interrupts: Should contain one interrupt shared by all channel.

- #dma-cells: must be <1>. Used to represent the number of integer

	cells in the dmas property of client device.

- #dma-channels : Number of DMA channels supported. Should be 32.

- clock-names: Should contain the clock of the DMA controller.

- clocks: Should contain a clock specifier for each entry in clock-names.

Example:

Controller:

apdma: dma-controller@20100000 {

	compatible = "sprd,sc9860-dma";

	reg = <0x20100000 0x4000>;

	interrupts = <GIC_SPI 50 IRQ_TYPE_LEVEL_HIGH>;

	#dma-cells = <1>;

	#dma-channels = <32>;

	clock-names = "enable";

	clocks = <&clk_ap_ahb_gates 5>;

};

Client:

DMA clients connected to the Spreadtrum DMA controller must use the format

described in the dma.txt file, using a two-cell specifier for each channel.

The two cells in order are:

1. A phandle pointing to the DMA controller.

2. The channel id.

spi0: spi@70a00000{

	...

	dma-names = "rx_chn", "tx_chn";

	dmas = <&apdma 11>, <&apdma 12>;

	...

};