libcopybit: Add Async mode support for C2D

- flush_get_fence API to copybit.h - which is async,
  which returns the fenceFD
- flush_get_fence calls C2dflush and c2dCreateFenceFD
  signals the c2d_wait_thread which waits for
  transcation to finish and cleanup resources

Change-Id: I98d5e08ea1cbce9732970c68c1e47b6f396249ce
3 files changed