ASoC: dapm: Use async I/O for DAPM sequences

ASoC: dapm: Use async I/O for DAPM sequences

Within a DAPM sequence we normally don't care about when exactly a register
write has completed so long as they happen in the order we requested. This
means that we can issue most of the writes we do asynchronously which
should maximise the ability of the underlying frameworks to keep the
hardware busy, providing a small performance improvement on some systems.

We currently ensure that all writes are completed both when changing to a
different device and when calling into the regulator and clock frameworks.
This should ensure that the previous ordering is maintained.

We also ensure that writes are completed prior to calling into widget
event functions since some event functions implement delays.  This
should be improved in future so that widgets can disable this sync in
order to add extra writes.

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