dt-bindings: spi: Add the DMA properties for the SPI dma mode

	address on the SPI bus. Should be set to 1.

- #size-cells: Should be set to 0.

Optional properties:

dma-names: Should contain names of the SPI used DMA channel.

dmas: Should contain DMA channels and DMA slave ids which the SPI used

	sorted in the same order as the dma-names property.

Example:

spi0: spi@70a00000{

	compatible = "sprd,sc9860-spi";

	interrupts = <GIC_SPI 7 IRQ_TYPE_LEVEL_HIGH>;

	clock-names = "spi", "source","enable";

	clocks = <&clk_spi0>, <&ext_26m>, <&clk_ap_apb_gates 5>;

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

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

	#address-cells = <1>;

	#size-cells = <0>;

};