ASoC: max98090: make it selectable

There is no way to select max98090 from menuconfig right now.
Add a Kconfig menu description to allow building the driver standalone.
It will allow this codec to be used by any other I2S master without
adding extra sound card entry in Kconfig.

Signed-off-by: Maxim Kochetkov <fido_max@inbox.ru>
Link: https://lore.kernel.org/r/20230421211950.20972-1-fido_max@inbox.ru


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