This patch changes the BVHCache implementation. It will use
a primitive array in stead of the ListBase. The locking is also
changed from a global lock to a per cache instance lock.
The performance of `gabby.blend` available on the cloud increased from 9.7
fps to 10.5 fps.
Reviewed By: Brecht van Lommel
Differential Revision: https://developer.blender.org/D7817
752139556f