Freescale Synchronous Audio Interface (SAI).

The SAI is based on I2S module that used communicating with audio codecs,
which provides a synchronous audio interface that supports fullduplex
serial interfaces with frame synchronization such as I2S, AC97, TDM, and
codec/DSP interfaces.


Required properties:
- compatible: Compatible list, contains "fsl,vf610-sai" or "fsl,imx6sx-sai".
- reg: Offset and length of the register set for the device.
- clocks: Must contain an entry for each entry in clock-names.
- clock-names : Must include the "bus" for register access and "mclk1" "mclk2"
  "mclk3" for bit clock and frame clock providing.
- dmas : Generic dma devicetree binding as described in
  Documentation/devicetree/bindings/dma/dma.txt.
- dma-names : Two dmas have to be defined, "tx" and "rx".
- pinctrl-names: Must contain a "default" entry.
- pinctrl-NNN: One property must exist for each entry in pinctrl-names.
  See ../pinctrl/pinctrl-bindings.txt for details of the property values.
- big-endian-regs: If this property is absent, the little endian mode will
  be in use as default, or the big endian mode will be in use for all the
  device registers.
- big-endian-data: If this property is absent, the little endian mode will
  be in use as default, or the big endian mode will be in use for all the
  fifo data.

Example:
sai2: sai@40031000 {
	      compatible = "fsl,vf610-sai";
	      reg = <0x40031000 0x1000>;
	      pinctrl-names = "default";
	      pinctrl-0 = <&pinctrl_sai2_1>;
	      clocks = <&clks VF610_CLK_PLATFORM_BUS>,
		     <&clks VF610_CLK_SAI2>,
		     <&clks 0>, <&clks 0>;
	      clock-names = "bus", "mclk1", "mclk2", "mclk3";
	      dma-names = "tx", "rx";
	      dmas = <&edma0 0 VF610_EDMA_MUXID0_SAI2_TX>,
		   <&edma0 0 VF610_EDMA_MUXID0_SAI2_RX>;
	      big-endian-regs;
	      big-endian-data;
};