Spreadtrum SPI Controller

Required properties:
- compatible: Should be "sprd,sc9860-spi".
- reg: Offset and length of SPI controller register space.
- interrupts: Should contain SPI interrupt.
- clock-names: Should contain following entries:
	"spi" for SPI clock,
	"source" for SPI source (parent) clock,
	"enable" for SPI module enable clock.
- clocks: List of clock input name strings sorted in the same order
	as the clock-names property.
- #address-cells: The number of cells required to define a chip select
	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";
	reg = <0 0x70a00000 0 0x1000>;
	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>;
};