Cycles: Make Embree compact BVH optional

Make the Embree RTC_SCENE_FLAG_COMPACT flag optional and enabled per default.
Disabling it makes CPU rendering a bit faster in some scenes at the cost of a higher memory usage.

Barbershop renders about 3% faster, victor about 4% on CPU with compact BVH disabled.

Differential Revision: https://developer.blender.org/D13592

intern/cycles/blender/sync.cpp

@@ -787,6 +787,7 @@ SceneParams BlenderSync::get_scene_params(BL::Scene &b_scene, bool background)
     params.bvh_type = BVH_TYPE_DYNAMIC;
 
   params.use_bvh_spatial_split = RNA_boolean_get(&cscene, "debug_use_spatial_splits");
+  params.use_bvh_compact_structure = RNA_boolean_get(&cscene, "debug_use_compact_bvh");
   params.use_bvh_unaligned_nodes = RNA_boolean_get(&cscene, "debug_use_hair_bvh");
   params.num_bvh_time_steps = RNA_int_get(&cscene, "debug_bvh_time_steps");