ASoC: fsl_sai: add tdm slots operation support

Add tdm slots operation support. If tdm slots and slot width have
been configured in machine driver, we should use these values.
Otherwise, using relevant channels and word length to set slots
and slot width.

SAI will generate BCLK depends on sample rate, slots and slot width.
And there may be unused BCLK cycles before each LRCLK transition.

Signed-off-by: Zidan Wang <zidan.wang@freescale.com>
Acked-by: Nicolin Chen <nicoleotsuka@gmail.com>
Signed-off-by: Mark Brown <broonie@kernel.org>