Blender Git Loki

OptiX: select BVH build options from Scene params

Currently, the OptiX BVH build options are selected based on whether
we are in background mode (final renders) or not (viewport renders).
In background mode, the BVH is built for fast path tracing and low
memory footprint, while in viewport, it is built for fast updates.

However, on platforms without OpenGL support, the background flag is
always set to true and prevents using fast BVH builds in the viewport.

Now, the BVH options derive from the Scene BVH settings:
* if BVH is static, a fast to trace BVH is built
* if BVH is dynamic, a fast to update BVH is built

Reviewed By: #cycles, brecht

Differential Revision: https://developer.blender.org/D11154