ASoC: dt-bindings: max98520: add initial bindings

add initial bindings for max98520 audio amplifier

Signed-off-by: George Song <george.song@maximintegrated.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20211027001431.363-1-george.song@maximintegrated.com


Signed-off-by: Mark Brown <broonie@kernel.org>