ASoC: Intel: Add ASoC Intel SST Atom sysfs description

For ASoC Intel SST Atom based devices a sysfs entry is created
in order to track FW version. The FW version is useful in order to
check the different Version of LPE DSP FW across Intel SoCs.

Signed-off-by: Sebastien Guiriec <sebastien.guiriec@intel.com>
Acked-by: Vinod Koul <vinod.koul@intel.com>
Signed-off-by: Mark Brown <broonie@kernel.org>