drm/i915: Refactor i915_gem_retire_requests()

Combine the iteration over active render rings into a common function.
This is in preparation for reusing the idle function to also retire
deferred free requests.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Eric Anholt <eric@anholt.net>
diff --git a/drivers/gpu/drm/i915/i915_drv.c b/drivers/gpu/drm/i915/i915_drv.c
index 119692f..5044f65 100644
--- a/drivers/gpu/drm/i915/i915_drv.c
+++ b/drivers/gpu/drm/i915/i915_drv.c
@@ -340,7 +340,7 @@
 	/*
 	 * Clear request list
 	 */
-	i915_gem_retire_requests(dev, &dev_priv->render_ring);
+	i915_gem_retire_requests(dev);
 
 	if (need_display)
 		i915_save_display(dev);