drm/i915: Split GEM resetting into 3 phases

drm/i915: Split GEM resetting into 3 phases

Currently we do a reset prepare/finish around the call to reset the GPU,
but it looks like we need a later stage after the hw has been
reinitialised to allow GEM to restart itself. Start by splitting the 2
GEM phases into 3:

  prepare - before the reset, check if GEM recovered, then stop GEM

  reset - after the reset, update GEM bookkeeping

  finish - after the re-initialisation following the reset, restart GEM

Signed-off-by: Chris Wilson <[email protected]>
Cc: Mika Kuoppala <[email protected]>
Reviewed-by: Mika Kuoppala <[email protected]>
Link: http://patchwork.freedesktop.org/patch/msgid/[email protected]
Link: http://patchwork.freedesktop.org/patch/msgid/[email protected]
(cherry picked from commit d80270931314a88d79d9bd5e0a5df93c12196375)
Signed-off-by: Jani Nikula <[email protected]>