ASoC: davinvi-mcasp: Proper suspend/resume support while audio is active

If the board is sent to suspend (deep sleep) the McASP context will be lost.
In case when suspend happens during active audio we need to save and restore
more registers, which was configured during hw_param times as well.
We need to add more config registers, AFIFO control registers and we also
need to save and restore the serializer configuration as well.
Since the number of serializers depends on the SoC we need to allocate the
memory for it based on the num_serializer for the given McASP instance.

With this patch the ongoing stream will resume after resuming from deep
sleep.

Signed-off-by: Peter Ujfalusi <peter.ujfalusi@ti.com>
Signed-off-by: Mark Brown <broonie@kernel.org>