ASoC: rt5651: Add rt5651_apply_properties() helper function

Move the applying of the differential input and dmic properties to a new
rt5651_apply_properties() helper function. This new function can be called
by platform code which attaches properties after probe() has run to apply
these new properties.

Note this also moves the time when we apply these properties for DT
platforms from i2c-probe to snd-component-probe time, this should not
result in any functional difference.

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