Allwinner A31/H3 SPI controller

Required properties:
- compatible: Should be "allwinner,sun6i-a31-spi" or "allwinner,sun8i-h3-spi".
- reg: Should contain register location and length.
- interrupts: Should contain interrupt.
- clocks: phandle to the clocks feeding the SPI controller. Two are
          needed:
  - "ahb": the gated AHB parent clock
  - "mod": the parent module clock
- clock-names: Must contain the clock names described just above
- resets: phandle to the reset controller asserting this device in
          reset

Optional properties:
- dmas: DMA specifiers for rx and tx dma. See the DMA client binding,
	Documentation/devicetree/bindings/dma/dma.txt
- dma-names: DMA request names should include "rx" and "tx" if present.

Example:

spi1: spi@01c69000 {
	compatible = "allwinner,sun6i-a31-spi";
	reg = <0x01c69000 0x1000>;
	interrupts = <0 66 4>;
	clocks = <&ahb1_gates 21>, <&spi1_clk>;
	clock-names = "ahb", "mod";
	resets = <&ahb1_rst 21>;
};

spi0: spi@01c68000 {
	compatible = "allwinner,sun8i-h3-spi";
	reg = <0x01c68000 0x1000>;
	interrupts = <GIC_SPI 65 IRQ_TYPE_LEVEL_HIGH>;
	clocks = <&ccu CLK_BUS_SPI0>, <&ccu CLK_SPI0>;
	clock-names = "ahb", "mod";
	dmas = <&dma 23>, <&dma 23>;
	dma-names = "rx", "tx";
	pinctrl-names = "default";
	pinctrl-0 = <&spi0_pins>;
	resets = <&ccu RST_BUS_SPI0>;
	#address-cells = <1>;
	#size-cells = <0>;
};