ASoC: rt5640: Allow specifying dmic data pins through device-properties

Allow specifying dmic data pins through device-properties / dt. This will
allow us to stop exporting rt5640_dmic_enable() once all callers of it have
been converted to setting device-properties for this instead.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Mark Brown <broonie@kernel.org>