[Intel-gfx] reduced LLC caching series

[Eric Anholt]

Chris posted a big patch series incorporating the cleaned up LLC
caching changes, but there were a bunch of not-ready-yet patches in
there.  This is a reduced series that I think is ready, with some
fixes from me.  From the final commit:

    Improves full-screen openarena on my laptop 20.3% +/- 4.0% (n=3)
    Improves 800x600 nexuiz on my laptop 12.3% +/- 0.1% (n=3)

Full screen, highest settings OA is now just about at refresh rate on
it.