Reduces the CPU overhead of descriptor set updates, which usually
happen once per draw call. Gains seem to be minor in most games,
some outliers show significantly better performance (i.e. Tomb Raider).
Fixes a few bottlenecks that were encountered in the Cascading Shadow
Maps demo from the Microsoft SDK. Performance is now slightly better
than wined3d with CSMT, MESA_NO_ERROR and mesa_glthread enabled.