ASoC: Intel: Skylake: Add shutdown callback

While going to shutdown, we need to bring HW to clean state. This
is done by cleaning up stream descriptor registers. This cleanup
is already done by decoupling of stream and stopping the chip, so
invoke these from shutdown handler.

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>