[Intel-gfx] GuC vs multiple timelines

[Chris Wilson]

Switching the GuC on for BAT testing another patch revealed I had broken
(made spammy at least) resets with requests in flight on the GuC. In the
course of fixing that, I kept tripping over a nasty timing issue in the
reuse of requests (with many threads running in parallel we would retire
a request whilst it was in the middle of the execute callback
elsewhere), so debug patches plus a small fix for that. And then there
were a few other issues found whilst looking at those...
-Chris