[Intel-gfx] Remaining set of small patches for -rc1

[Chris Wilson]

A couple of patches to tidy the merge with atomic modesetting. 2 patches
to fix the offset page-flipping. A patch to workaround one common cause of
hangs after modesetting whilst page-flipping, it's not the full patch but
it should prevent the hang in 99% of cases [statistic made up on the
spot], and with the additional reset in hangcheck should prevent a fatal
hang on i915. A couple of trivial patches that should help with a couple
of bugs. And the most fun, the asynchronous fbdev init which has been
tested by Meego and a few other adventurous fast booters.