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

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

Signed-off-by: Jie Yang <yang.jie@intel.com>
Acked-by: Vinod Koul <vinod.koul@intel.com>
Signed-off-by: Mark Brown <broonie@kernel.org>