drm/i915: Move gpu_write_list to per-ring

... to prevent flush processing of an idle (or even absent) ring.

This fixes a regression during suspend from 87acb0a5.

Reported-and-tested-by: Alexey Fisher <bug-track@fisher-privat.net>
Tested-by: Peter Clifton <pcjc2@cam.ac.uk>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.c b/drivers/gpu/drm/i915/intel_ringbuffer.c
index 4b53ca8..09f2dc3 100644
--- a/drivers/gpu/drm/i915/intel_ringbuffer.c
+++ b/drivers/gpu/drm/i915/intel_ringbuffer.c
@@ -580,6 +580,7 @@
 	ring->dev = dev;
 	INIT_LIST_HEAD(&ring->active_list);
 	INIT_LIST_HEAD(&ring->request_list);
+	INIT_LIST_HEAD(&ring->gpu_write_list);
 
 	if (I915_NEED_GFX_HWS(dev)) {
 		ret = init_status_page(dev, ring);