ASoC: Intel: Skylake: Constrain the audio devices

In ref configuration for Skylake, we support only 16bit, 48KHz,
stereo audio, so specify these as constrains for the devices

Signed-off-by: Jeeja KP <jeeja.kp@intel.com>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>
Signed-off-by: Mark Brown <broonie@kernel.org>