drm/i915: capture error_state also for stuck rings

Since quite a while we also the basic output configuration in the
error_state, so it should contain enough information to diagnose
these MI_WAIT hangs.

Reviewed-and-tested-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Eugeni Dodonov <eugeni.dodonov@intel.com>
Signed-Off-by: Daniel Vetter <daniel.vetter@ffwll.ch>