[Intel-gfx] vlv punit and sideband tidy

[Chris Wilson]

While we continue to observe hangs even with this w/a in place, I do
believe we are in a better position (although that may just be my
confirmation bias). I certainly don't think it's all happy yet. Mika
believes that if we keep the cpu in C0 whilst the gpu is busy, then it
behaves much better -- but that is a very tough sell; virtually disabling
cpu powersaving entirely, for the gpu rarely sleeps under the target
workloads.

Still I think this series moves us forwards and would appreciation acks
or an outright nak to drop it. :)
-Chris