Blender Git Loki

Revert "Cycles: Cleanup, move Embree BVH logic to own file"

While we shouldn't have logic in an entry point, and since one should
not be making typos when moving lines around, there is bigger entanglement
issue with BVH host code using kernel function. This is bad violation,
but is tricky to get solved moments before the weekly.

In order to keep things in a (less) broken state than before own cleanup
reverting the changes.

This reverts commit 2bad10be96540ff50a149230d656e599775b3f47.
This reverts commit ddabb21d0584e9874e8e5c62c04abe496ec7334b