During suspend flow, sof_suspend will be called and the pm_ops->ctx_save
callback notifies DSP of the upcoming power down.

Upon receipt of the ctx_save IPC, the DSP will start the D3 transition.
Before the DSP enter idle, an interrupt is generated to notify the host of
the power state change.

Since the host and DSP are two different processors, there could be a
race condition, which can be avoided by polling with 1s timeout and 500us
intervals
Reviewed-by: Péter Ujfalusi <peter.ujfalusi@linux.intel.com>
Signed-off-by: YC Hung <yc.hung@mediatek.com>
Signed-off-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Link: https://lore.kernel.org/r/20220606210212.146626-6-pierre-louis.bossart@linux.intel.comSigned-off-by: Mark Brown <broonie@kernel.org>