ASoC: dt-bindings: add rockchip i2s bindings

Add devicetree bindings for i2s controller found on
rk3066, rk3188 and rk3288 processors from rockchip.
Signed-off-by: Jianqun Xu <xjq@rock-chips.com>
Signed-off-by: NMark Brown <broonie@linaro.org>

Documentation/devicetree/bindings/sound/rockchip-i2s.txt

+* 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.
+- #address-cells: should be 1.
+- #size-cells: should be 0.
+- 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
+
+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>;
+	#address-cells = <1>;
+	#size-cells = <0>;
+	dmas = <&pdma1 0>, <&pdma1 1>;
+	dma-names = "rx", "tx";
+	clock-names = "i2s_hclk", "i2s_clk";
+	clocks = <&cru HCLK_I2S0>, <&cru SCLK_I2S0>;
+};