ASoC: dt-bindings: Add schema for "awinic,aw8738"

ASoC: dt-bindings: Add schema for "awinic,aw8738"

Add a DT schema for describing Awinic AW8738 audio amplifiers. They are
fairly simple and controlled using a single GPIO. The number of pulses
during power up selects one of a few pre-defined operation modes. This
can be used to configure the speaker-guard function (primarily the
power limit for the amplifier).

Signed-off-by: Stephan Gerhold <stephan@gerhold.net>
Link: https://lore.kernel.org/r/20220304102452.26856-2-stephan@gerhold.net
Signed-off-by: Mark Brown <broonie@kernel.org>