[Intel-gfx] A picking of low hanging fruit

[Chris Wilson]

I was looking at the performance degredation due to execlists and
decided to pick a few of the easier microoptimisations. Individually
they may not amount to much (except for spinning on requests!) but the
volume does quickly add up, giving benefit to quite a few of our more
driver bound tests.

Almost all of these I have posted before.
-Chris