ASoC: Added device tree binding for max98373 amplifier

Maxim Integrated MAX98373 Speaker Amplifier

This device supports I2C.

Required properties:

 - compatible : "maxim,max98373"

 - reg : the I2C address of the device.

Optional properties:

  - maxim,vmon-slot-no : slot number used to send voltage information

                   or in inteleave mode this will be used as

                   interleave slot.

                   slot range : 0 ~ 15,  Default : 0

  - maxim,imon-slot-no : slot number used to send current information

                   slot range : 0 ~ 15,  Default : 0

  - maxim,spkfb-slot-no : slot number used to send speaker feedback information

                   slot range : 0 ~ 15,  Default : 0

  - maxim,interleave-mode : For cases where a single combined channel

		   for the I/V sense data is not sufficient, the device can also be configured

		   to share a single data output channel on alternating frames.

		   In this configuration, the current and voltage data will be frame interleaved

		   on a single output channel.

                   Boolean, define to enable the interleave mode, Default : false

Example:

codec: max98373@31 {

   compatible = "maxim,max98373";

   reg = <0x31>;

   maxim,vmon-slot-no = <0>;

   maxim,imon-slot-no = <1>;

   maxim,spkfb-slot-no = <2>;

   maxim,interleave-mode;

};