ASoC: dt-bindings: codecs: Add bindings for ak4375

AK4375 is an audio DAC with headphones amplifier controlled via I2C.
Add simple device tree bindings that describe how to set it up.

Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Vincent Knecht <vincent.knecht@mailoo.org>
Link: https://lore.kernel.org/r/20211220193725.2650356-1-vincent.knecht@mailoo.org


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