ASoC: SOF: Intel: ipc4: Wait for channel to be free before sending a message

ASoC: SOF: Intel: ipc4: Wait for channel to be free before sending a message

Before attempting to send a message to the DSP we need to check if the
downstream BUSY flag has been cleared by the firmware to avoid lost IPC
messages by the firmware.

This is required by a firmware which only acks the received message after
it has sent a reply to the host.
With a bad luck, the host would send a message before the firmware gets to
the clearing the flag and thus losing a message.

Signed-off-by: Peter Ujfalusi <peter.ujfalusi@linux.intel.com>
Reviewed-by: Kai Vehmanen <kai.vehmanen@linux.intel.com>
Reviewed-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Reviewed-by: Ranjani Sridharan <ranjani.sridharan@linux.intel.com>
Reviewed-by: Rander Wang <rander.wang@intel.com>
Link: https://lore.kernel.org/r/20221018124008.6846-4-peter.ujfalusi@linux.intel.com
Signed-off-by: Mark Brown <broonie@kernel.org>