ASoC: dt-bindings: Add schema for "awinic,aw87390"

Add a DT schema for describing awinic aw87390 audio amplifiers.
They are controlled using I2C.

Signed-off-by: Weidong Wang <wangweidong.a@awinic.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20230928105727.47273-3-wangweidong.a@awinic.com


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