aaudio: reduce glitching by improving sleep timing

ALways sleep a minimum time to avoid busy wait in real-time thread.
Account for wakeup jitter in threads on the other side of a FIFO.
Avoid race condition that caused a longer sleep than necessary.
Fix calculation of mFreeRunning for capture mode.

Also added systrace logging, which was used to debug this.

Bug: 63814792
Test: Run GStomper on Walleye with MMAP on, see bug
Change-Id: I7b20098580ff454365425bd21e43c17ade532a0a