[Intel-gfx] FBC patchset

[Chris Wilson]

This is hopefully the culimination of yesterday's patches and review. I
pulled in Jesse's comments about needing to be sure that the tasklet was
not running on module unload and after several prods by Keith, we have
safely eliminated any potential blocking waits on vblank when changing
FBC configurations. As always further feedback is welcome. The one
remaining question I have is over the use of 50ms as the delay interval.
It was a value that was just sufficiently large enough to cover
page-flipping, but maybe we are better with a less agressive 100ms for
the purposes of "letting the display settle" before compressing the
scanout?
-Chris