sde-drm: Protect access to tmp_prop_val_map_ to avoid crash

DRMPlane's map (tmp_prop_val_map_) can be accessed by multiple
threads simultaneously which can cause deadlocks or segfault
errors. This changes adds a mutex lock to protect access to
the object to avoid such scenarios.

Change-Id: I8bc4de83a9fd24d431739f811b0297ba84b1fd83
CRs-Fixed: 3275492
1 file changed