ASoC: SOF: add a flag to indicate the system suspend target

Add flag 's0_suspend' to indicate if the system is entering S0ix or
not.

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/20191025224122.7718-20-pierre-louis.bossart@linux.intel.com


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