Blender Git Loki

GPUPass: Refactor gpupass caching system to allow fast gpumaterial creation.

This is part of the work needed to refactor the material parameters update.

Now the gpupass cache is polled before adding the gpumaterial to the
deferred compilation queue.

We store gpupasses in a single linked list grouped based on their hashes.
This is not the most efficient way but it can be improved upon later.