drm/i915: Clean up bo lists on all hung gpus

Previously we only tidied up the active bo lists for chipsets were we
would attempt to reset the GPU. However, this action is necessary for
the system to continue and reclaim the dead bo for all chipsets.

Pointed out, in passing, by Owain Ainsworth.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>