[Ozone-Drm] Add log message when the DRM device is authenticated

It makes it possible to tell if the GPU process is stuck waiting
for a DRM device to authenticate.

BUG=476728

Review URL: https://codereview.chromium.org/1086353003

Cr-Commit-Position: refs/heads/master@{#325486}

ui/ozone/platform/drm/gpu/drm_device.cc

@@ -232,6 +232,8 @@ bool DrmDevice::Initialize() {
         << "': " << base::File::ErrorToString(file_.error_details());
   }
 
+  VLOG(1) << "Succeeded in taking master on " << device_path_.value();
+
 #if defined(USE_DRM_ATOMIC)
   plane_manager_.reset(new HardwareDisplayPlaneManagerAtomic());
 #else