* Rockchip I2S controller

The I2S bus (Inter-IC sound bus) is a serial link for digital
audio data transfer between devices in the system.

Required properties:

- compatible: should be one of the followings
   - "rockchip,rk3066-i2s": for rk3066
   - "rockchip,rk3188-i2s", "rockchip,rk3066-i2s": for rk3188
   - "rockchip,rk3288-i2s", "rockchip,rk3066-i2s": for rk3288
- reg: physical base address of the controller and length of memory mapped
  region.
- interrupts: should contain the I2S interrupt.
- dmas: DMA specifiers for tx and rx dma. See the DMA client binding,
	Documentation/devicetree/bindings/dma/dma.txt
- dma-names: should include "tx" and "rx".
- clocks: a list of phandle + clock-specifer pairs, one for each entry in clock-names.
- clock-names: should contain followings:
   - "i2s_hclk": clock for I2S BUS
   - "i2s_clk" : clock for I2S controller
- rockchip,playback-channels: max playback channels, if not set, 8 channels default.
- rockchip,capture-channels: max capture channels, if not set, 2 channels default.

Example for rk3288 I2S controller:

i2s@ff890000 {
	compatible = "rockchip,rk3288-i2s", "rockchip,rk3066-i2s";
	reg = <0xff890000 0x10000>;
	interrupts = <GIC_SPI 85 IRQ_TYPE_LEVEL_HIGH>;
	dmas = <&pdma1 0>, <&pdma1 1>;
	dma-names = "tx", "rx";
	clock-names = "i2s_hclk", "i2s_clk";
	clocks = <&cru HCLK_I2S0>, <&cru SCLK_I2S0>;
	rockchip,playback-channels = <8>;
	rockchip,capture-channels = <2>;
};