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

Add the DMA properties for the SPI dma mode.
Signed-off-by: Lanqing Liu <lanqing.liu@unisoc.com>
Signed-off-by: Baolin Wang <baolin.wang@linaro.org>
Signed-off-by: Mark Brown <broonie@kernel.org>

Documentation/devicetree/bindings/spi/spi-sprd.txt

@@ -14,6 +14,11 @@ Required properties:
 	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";
@@ -21,6 +26,8 @@ spi0: spi@70a00000{
 	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>;
 };