drm_hwcomposer: Ensure composer has master access to DRM/KMS
Allocator service is always loaded before Composer service. Kernel will assign master access to the first client that opened /dev/dri/cardX node.
Allocator should immediately execute drmDropMaster() to allow Composer service to acquire master privileges.
If this does not happen, the composer should gracefully exit, otherwise a lot of DRM ioctls will fail without displaying anything on the UI.