ASoC: simple-amplifier: Introduce support for gpio-audio-amp

ASoC: simple-amplifier: Introduce support for gpio-audio-amp

Improve the simple-amplifier introducing preliminary support for
gpio-audio-amp.

Those amplifiers are amplifiers driven by gpios.

This support introduction doesn't handle any GPIO yet but introduces
the compatible strings and the related DAPM table.

Two gpio-audio-amp are available: A mono and a stereo version.

The mono version has only one audio channel and gpio settings impact
features such as the gain or mute of this sole channel.

The stereo version has two channels (left and right). Gpio settings
impact both channels in the same manner and at the same time. For
instance, the gain setting set the gain of both channels as well as
the mute setting mutes both channels.

Signed-off-by: Herve Codina <herve.codina@bootlin.com>
Link: https://patch.msgid.link/20260513081702.317117-10-herve.codina@bootlin.com
Signed-off-by: Mark Brown <broonie@kernel.org>