ASoC: pcm3168a: Implement set_tdm_slot callback

Initially we only going to care about the slot_width as for example
DSP_A/B needs 32 bclk per slots and to be able to use TDM mode the codec
(and CPU) needs to use DSP_A/B modes.

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