ASoC: SOF: Intel: add module namespace for legacy IPC

The legacy IPC routines are only used by broadwell and baytrail
modules, import them as needed and make sure other modules cannot load
them.

Signed-off-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Link: https://lore.kernel.org/r/20191217202231.18259-2-pierre-louis.bossart@linux.intel.com


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