Blender Git Loki

Cycles OpenCL: Motion Blur Compile Directives

When using preview rendering through a camera or final rendering
the `scene.render.use_motion_blur` was not respected when building
the compile directives.

This patch will when building the compile directives check if
motion blur is enabled at all. This should lead to more efficient
kernels when no motion blur is needed.

Tags: #cycles

Differential Revision: https://developer.blender.org/D4387