WM8741 audio CODEC

This device supports both I2C and SPI (configured with pin strapping
on the board).

Required properties:

  - compatible : "wlf,wm8741"

  - reg : the I2C address of the device for I2C, the chip select
          number for SPI.

Optional properties:

  - diff-mode: Differential output mode configuration. Default value for field
    DIFF in register R8 (MODE_CONTROL_2). If absent, the default is 0, shall be:
    0 = stereo
    1 = mono left
    2 = stereo reversed
    3 = mono right

Example:

codec: wm8741@1a {
	compatible = "wlf,wm8741";
	reg = <0x1a>;

	diff-mode = <3>;
};