ASoC: SOF: Provide probe debugfs support

Define debugfs subdirectory delegated for IPC communication with DSP.
Input format: uint,uint,(...) which are later translated into DWORDS
sequence and further into instances of struct of interest given the IPC
type.

For Extractor probes, following have been enabled:
- PROBE_POINT_ADD (echo <..> probe_points)
- PROBE_POINT_REMOVE (echo <..> probe_points_remove)
- PROBE_POINT_INFO (cat probe_points)

Signed-off-by: Cezary Rojewski <cezary.rojewski@intel.com>
Acked-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Link: https://lore.kernel.org/r/20200218143924.10565-9-cezary.rojewski@intel.com
Signed-off-by: Mark Brown <broonie@kernel.org>