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
diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
index 4ebd3ff..a93e5dd 100644
--- a/drivers/gpu/drm/i915/i915_drv.h
+++ b/drivers/gpu/drm/i915/i915_drv.h
@@ -495,6 +495,7 @@
 		u32 cpu_ring_head;
 		u32 cpu_ring_tail;
 
+		u32 last_seqno;
 		u32 semaphore_seqno[I915_NUM_ENGINES - 1];
 
 		/* Register state */