sde: Implement sequence locker to lock across multiple APIs.

1. Lock prepare() and set() APIs using sequence entry and sequence
   exit lock respectively to prevent the critical section being
   accessed by other threads.
2. Wait for sequence wait lock on HotPlugEvent thread or any other
   binder threads(Eg. dumpsys), before it accesses the critical region.
3. Prevent deadlock during multiple prepare() calls before a set().

Change-Id: I5443675c870ed2967615ec383dd2d59ded30b52b
2 files changed