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: Boolean property, required if all the FTM_PWM registers
  are big-endian rather than little-endian.
- lsb-first: Configures whether the LSB or the MSB is transmitted first for
  the fifo data. If this property is absent, the MSB is transmitted first as
  default, or the LSB is transmitted first.
- fsl,sai-synchronous-rx: This is a boolean property. If present, indicating
  that SAI will work in the synchronous mode (sync Tx with Rx) which means
  both the transimitter and receiver will send and receive data by following
  receiver's bit clocks and frame sync clocks.
- fsl,sai-asynchronous: This is a boolean property. If present, indicating
  that SAI will work in the asynchronous mode, which means both transimitter
  and receiver will send and receive data by following their own bit clocks
  and frame sync clocks separately.

Note:
- If both fsl,sai-asynchronous and fsl,sai-synchronous-rx are absent, the
  default synchronous mode (sync Rx with Tx) will be used, which means both
  transimitter and receiver will send and receive data by following clocks
  of transimitter.
- fsl,sai-asynchronous and fsl,sai-synchronous-rx are exclusive.

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;
	      lsb-first;
};
