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_debugfs.c b/drivers/gpu/drm/i915/i915_debugfs.c
index 1e8cd74..addb939 100644
--- a/drivers/gpu/drm/i915/i915_debugfs.c
+++ b/drivers/gpu/drm/i915/i915_debugfs.c
@@ -684,6 +684,9 @@
 	seq_printf(m, "  INSTPM: 0x%08x\n", error->instpm);
 	seq_printf(m, "  seqno: 0x%08x\n", error->seqno);
 
+	for (i = 0; i < 16; i++)
+		seq_printf(m, "  fence[%d] = %08llx\n", i, error->fence[i]);
+
 	if (error->active_bo)
 		print_error_buffers(m, "Active",
 				    error->active_bo,