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",
			  "fsl,imx6sx-sai", "fsl,imx6ul-sai",
			  "fsl,imx7ulp-sai", "fsl,imx8mq-sai" or
			  "fsl,imx8qm-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.

  - 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 transmitter and the
			  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 transmitter and receiver will send and
			  receive data by following their own bit clocks and
			  frame sync clocks separately.

Optional properties:

  - big-endian		: Boolean property, required if all the SAI
			  registers are big-endian rather than little-endian.

Optional properties (for mx6ul):

  - fsl,sai-mclk-direction-output: This is a boolean property. If present,
			 indicates that SAI will output the SAI MCLK clock.

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
  transmitter and receiver will send and receive data by following clocks
  of transmitter.
- 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;
};