[Intel-gfx] RPS tuning

[Chris Wilson]

I have so many outstanding patches, that my smtp relay reject them for
being a spamhost...

These are the simple patches for further tuning RPS to begin with. 5
trivial/bug fixes, a couple of patches for read-read concurrency, and 
then 8 patches to both limit the number of RPS boosts on systems without
semaphore support (*cough* Broadwell *cough*) and then one to prevent
downclocking whilst clients are still waiting, along with a boost for
severe stalls. Finally the icing on the cake is enabling waitboosting
for Ironlake.
-Chris