sde-drm: introduce lock for synchronization.

- map values (i.e, tmp_prop_val_map_) may accessible
  from two threads for below calls and cause race condition.
  i) on UnRegisterDisplay
  ii) on Prepare/Commit/Perform

Change-Id: Icf2d868bd0928725f62f8b7cd4b4d4ab95a251e2
CRs-Fixed: 2422570
4 files changed