drm/i915: Record fence registers on error.

Having seen the effects of erroneous fencing on the batchbuffer, a
useful sanity check is to record the fence registers at the time of an
error.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
index 22d6388..699e71a 100644
--- a/drivers/gpu/drm/i915/i915_drv.h
+++ b/drivers/gpu/drm/i915/i915_drv.h
@@ -166,6 +166,7 @@
 	u32 instdone1;
 	u32 seqno;
 	u64 bbaddr;
+	u64 fence[16];
 	struct timeval time;
 	struct drm_i915_error_object {
 		int page_count;