drm/i915: Capture PPGTT info on error capture

v2: Rebased upon cleaned up error state
v3: Make sure hangcheck info remains last (Chris)

Cc: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Ben Widawsky <ben@bwidawsk.net>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>