Blender Git Loki

Cycles: Make OptiX device compilable

- Follows the regular structure of CPU and CUDA directory.
- Use Cycles-style comment style, use explicit code blocks when
was easy to spot.
- Use common implementation of CUDAContextScope.
- Remove calls from header which were removed from other devices.
- Comment out all implementation methods.

All in all, this is a CUDA device at this time. The actual OptiX
parts will be brought back as a followup development.