Cycles CUDA: don't use cuLaunchGridAsync at all for display devices.
Cycles CUDA: don't use cuLaunchGridAsync at all for display devices.

As suggested by Martijn, this is slower than cuLaunchGrid.

pyrochlore/cycles,tangent-opensource/coreBlackbird,tangent-opensource/coreBlackbird,tangent-opensource/coreBlackbird,pyrochlore/cycles,pyrochlore/cycles