ASoC: SOF: Add DSP HW abstraction operations

Add operation pointers that can be called by core to control a wide
variety of DSP targets. The DSP HW drivers will fill in these
operations.

Signed-off-by: Liam Girdwood <liam.r.girdwood@linux.intel.com>
Signed-off-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Reviewed-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Mark Brown <broonie@kernel.org>