ASoC: Intel: Skylake: Await purge request ack on CNL

ASoC: Intel: Skylake: Await purge request ack on CNL

Each purge request is sent by driver after master core is powered up and
unresetted but before it is unstalled. On unstall, ROM begins processing
the request and initializing environment for FW load. Host should await
ROM's ack before moving forward. Without doing so, ROM init poll may
start too early and false timeouts can occur.

Fixes: 9a1cb1e8c51d ("ASoC: Intel: cnl: Add sst library functions for cnl platform")
Signed-off-by: Cezary Rojewski <cezary.rojewski@intel.com>
Reviewed-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Link: https://lore.kernel.org/r/20200305145314.32579-8-cezary.rojewski@intel.com
Signed-off-by: Mark Brown <broonie@kernel.org>