Blender Git Loki

Cycles: Initial support of 3D textures for CUDA rendering

Supports both smoke/fire and point density textures now.

Reduces number of textures available for sm_20 and sm_21, but you have
to compromise somewhere on such a limited hardware.

Currently limited to linear interpolation only, and decoupled ray
marching is not supported yet. Think those could be considered just a
further improvement.

Some quick example:

https://developer.blender.org/F282934

Code is minimal and we can fully consider it a fix for missing
support of 3D textures with CUDA.

Reviewers: lukasstockner97, brecht, juicyfruit, dingto

Reviewed By: brecht, juicyfruit, dingto

Subscribers: mib2berlin

Differential Revision: https://developer.blender.org/D1806