ASoC: Intel: create baytrail folder and move baytrail platform files in

Restructure the sound/soc/intel/ directory: create baytrail folder, and move
sst baytrail platform files here.

Signed-off-by: Jie Yang <yang.jie@intel.com>
Acked-by: Jarkko Nikula <jarkko.nikula@linux.intel.com>
Tested-by: Jarkko Nikula <jarkko.nikula@linux.intel.com>
Signed-off-by: Mark Brown <broonie@kernel.org>