ASoC: dt-bindings: ti,pcm1754: add binding documentation

ASoC: dt-bindings: ti,pcm1754: add binding documentation

The Texas Instruments PCM1754 is a simple stereo DAC without any digital
management interface but soft mute, PCM input format and 44.1 kHz
digital de-emphasis can be configured via strapping pins. Only soft mute
and PCM input format selection is currently exposed via optional GPIOs
in the driver.

Signed-off-by: Stefan Kerkmann <s.kerkmann@pengutronix.de>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://patch.msgid.link/20250910-v6-12-topic-pcm1754-v2-1-0917dbe73c65@pengutronix.de
Signed-off-by: Mark Brown <broonie@kernel.org>