audioflinger: refactor thread config events

Merge config events and set parameters messaging mechanism.
- setting parameters now uses the config event mechanism
- config event now allow to wait for a condition and synchronize caller
binder thread with execution thread and return an execution status.
- simplify locking mechanism to avoid unlocking the thread
mutex while processing events.

Change-Id: Ia49cb3e617abec4bacb6c1f9a8cb304c4ed3902e