drm/i915: Include engine->last_submitted_seqno in GPU error state

drm/i915: Include engine->last_submitted_seqno in GPU error state

It's useful to look at the last seqno submitted on a particular engine
and compare it against the HWS value to check for irregularities.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Reviewed-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1460010558-10705-1-git-send-email-chris@chris-wilson.co.uk