ASoC: dt-bindings: Added schema for "nuvoton,nau8325"

ASoC: dt-bindings: Added schema for "nuvoton,nau8325"

Add a DT schema for describing nau8325 audio amplifiers. The key features
are as follows:
  - Low SPK_VDD Quiescent Current
  - Gain Setting with 2-wire interface
  - Powerful Stereo Class-D Amplifier
  - Low Output Noise
  - Low Current Shutdown Mode
  - Click-and Pop Suppression

More resources :
https://www.nuvoton.com/products/smart-home-audio/audio-amplifiers/class-d-series/nau8325yg/

Signed-off-by: Seven Lee <wtli@nuvoton.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Link: https://msgid.link/r/20240327075755.3410381-2-wtli@nuvoton.com
Signed-off-by: Mark Brown <broonie@kernel.org>