Blender Git Loki

Cycles: Refactor KernelFunctions class

- Rename it toKernelFunction with a comment which makes it explicit
that it is a single kernel, which picks up best microarchitecture
for the current configuration.

- Re-write initialization part, avoiding chain of code-wise if-else
mixed together with preprocessor.

Some further possibilities:

- Avoid preprocessor check, and rely on settings and function pointers
to pick up best kernel, avoiding preprocessor.

- Use string_view or something similar instead of `char*` to make
comparison more modern.