ASoC: Intel: kbl_rt5663_rt5514_max98927: Add dmic format constraint

On KBL platform, the microphone is attached to external codec(rt5514)
instead of PCH. However, TDM slot between PCH and codec is 16 bits only.
In order to avoid setting wrong format, we should add a constraint to
force to use 16 bits format forever.

Signed-off-by: Yu-Hsuan Hsu <yuhsuan@chromium.org>
Acked-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Link: https://lore.kernel.org/r/20190923162940.199580-1-yuhsuan@chromium.org


Signed-off-by: Mark Brown <broonie@kernel.org>