Hearing Aid: Remove std::promise from suspend / resume calls, and stop audio ticks by no devices

The Hearing Aid uses the stack main thread to be the media task thread.
This thread handles events / feeds audio data sequentially, and won't
have a race condition within the single thread. The promise is a bit
redundant, but wasted time to cause a potential deadlock that the caller
waits for the task thread finished which needed the caller's resource.

This CL also stops the audio ticks when no devices available, and no
need to wait for next timer expired. Besides, move all timer controls
into the media task thread, so timer is started / stopped at the same
thread, too.

Bug: 134996542
Test: add big delay within functions, and check no abnormal manually
Change-Id: If0b279a191d86b30db41a682dc7f0ad9470cb10e