ASoC: rt5640: Make codec selectable

The Realtek rt5640 codec driver can be used with the generic sound card
drivers, so it should be selectable. For example, with the addition
of #sound-dai-cells = <0> property in DT, it can be used with simple and
graph card drivers.

Signed-off-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Link: https://lore.kernel.org/r/20210612200650.1301661-1-martin.blumenstingl@googlemail.com


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