Blender Git Loki

Cycles: enable Embree by default for CPU rendering

For GPU debugging purposes, it is still possible to render with the same BVH2
on the CPU using the Debug panel in the render properties.

Note that building Blender without Embree will now lead to significantly reduced
performance in CPU rendering, and a few of the Cycles regression tests will fail
due to small pixel differences.

Ref T73778

Depends on D8014

Maniphest Tasks: T73778

Differential Revision: https://developer.blender.org/D8015