ASoC: davinci-mcasp: Place constraint on number of channels

In IIS (I2S, TDM, etc) mode the maximum number of allowed channels for
either direction can be:
number of serializers for the direction * tdm_slots.
This constraint applicable for the first stream, while consequent stream
should not have more channels then the first stream.

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