ASoC: SOF: Intel: add namespace for XTENSA

Now that Xtensa stuff is only referenced in Intel stuff, define
namespace and import it in Intel BYT/BDW/HDaudio modules

Signed-off-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Link: https://lore.kernel.org/r/20191217202231.18259-9-pierre-louis.bossart@linux.intel.com


Signed-off-by: Mark Brown <broonie@kernel.org>