ASoC: ti: davinci-mcasp: Improve serializer handling in multi AXR setups

ASoC: ti: davinci-mcasp: Improve serializer handling in multi AXR setups

When multiple serializers are used we need to track the number of
serializers used by the other stream direction to avoid killing data lines
when the first stream used more serializers than the second would need.
We are still protected against the case when the second stream uses more
serializers which had affected the running stream as well.

To take advantage of the improved serializer logic we need to modify the
channel constraints rule as well to allow the use of multiple serializers
for the second stream as additional ones will not affect the FS/BCLK on
the bus.

Signed-off-by: Peter Ujfalusi <peter.ujfalusi@ti.com>
Link: https://lore.kernel.org/r/20190725083432.7419-1-peter.ujfalusi@ti.com
Signed-off-by: Mark Brown <broonie@kernel.org>