This change brings back old original logic which was checking
whether worker threads do fit into an active CPU group. But
it does it a bit smarter now and is also checking affinity
within that group. This way Cycles will use all threads on a
Threadripper2 CPU if it's set to automatic number of threads,
but on another hand will not change affinity if user requested
16 threads and changed Blender affinity.
Sergey Sharybin
48506a3431