ASoC: SOF: PM: add helpers for setting D0 substate for ADSP

Add snd_sof_set_d0_substate() helper for setting ADSP to a specific D0
substate, it will call into the platform specific implementation, and
update the d0_substate at success.

Signed-off-by: Keyon Jie <yang.jie@linux.intel.com>
Signed-off-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Link: https://lore.kernel.org/r/20191025224122.7718-18-pierre-louis.bossart@linux.intel.com


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