ASoC: codecs: allow SSM2518 to be selected by the user

Allow the Analog SSM2518 driver to be enabled without a large
bunch of other drivers.

Signed-off-by: Lucas Stach <l.stach@pengutronix.de>
Link: https://lore.kernel.org/r/20210628210458.2508973-1-l.stach@pengutronix.de


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