ASoC: SOF: Use high-priority workqueue for PCM period elapsed

The snd_sof_pcm_period_elapsed function currently schedules work on the
system-wide workqueue. This can lead to potential delays or jitter in
audio processing if the system workqueue is busy with other tasks.

To improve real-time performance and ensure timely processing of PCM
periods, we can use the system_highpri_wq instead of the default work
queue.

In performance testing, this change significantly reduced the observed
scheduling delays. For instance, under load(stressapptest -M 15000 -m
60), the maximum delay dropped from 9ms on the system workqueue to 5ms
on the dedicated high-priority workqueue.

Author: Yu-Hsuan Hsu

sound/soc/sof/pcm.c

@@ -62,7 +62,7 @@ void snd_sof_pcm_period_elapsed(struct snd_pcm_substream *substream)
 	 * To avoid sending IPC before the previous IPC is handled, we
 	 * schedule delayed work here to call the snd_pcm_period_elapsed().
 	 */
-	schedule_work(&spcm->stream[substream->stream].period_elapsed_work);
+	queue_work(system_highpri_wq, &spcm->stream[substream->stream].period_elapsed_work);
 }
 EXPORT_SYMBOL(snd_sof_pcm_period_elapsed);