* Rockchip SPDIF transceiver

The S/PDIF audio block is a stereo transceiver that allows the
processor to receive and transmit digital audio via an coaxial cable or
a fibre cable.

Required properties:

- compatible: should be one of the following:
   - "rockchip,rk3066-spdif"
   - "rockchip,rk3188-spdif"
   - "rockchip,rk3228-spdif"
   - "rockchip,rk3288-spdif"
   - "rockchip,rk3328-spdif"
   - "rockchip,rk3366-spdif"
   - "rockchip,rk3368-spdif"
   - "rockchip,rk3399-spdif"
- reg: physical base address of the controller and length of memory mapped
  region.
- interrupts: should contain the SPDIF interrupt.
- dmas: DMA specifiers for tx dma. See the DMA client binding,
  Documentation/devicetree/bindings/dma/dma.txt
- dma-names: should be "tx"
- clocks: a list of phandle + clock-specifier pairs, one for each entry
  in clock-names.
- clock-names: should contain following:
   - "hclk": clock for SPDIF controller
   - "mclk" : clock for SPDIF bus

Required properties on RK3288:
  - rockchip,grf: the phandle of the syscon node for the general register
                   file (GRF)

Example for the rk3188 SPDIF controller:

spdif: spdif@0x1011e000 {
	compatible = "rockchip,rk3188-spdif", "rockchip,rk3066-spdif";
	reg = <0x1011e000 0x2000>;
	interrupts = <GIC_SPI 32 IRQ_TYPE_LEVEL_HIGH>;
	dmas = <&dmac1_s 8>;
	dma-names = "tx";
	clock-names = "hclk", "mclk";
	clocks = <&cru HCLK_SPDIF>, <&cru SCLK_SPDIF>;
	#sound-dai-cells = <0>;
};