drm/i915: Remove early exit on i915_gpu_idle

[Description from: Daniel Vetter]
I've just discussed this quickly with Chris on irc and it's probably
best to just kill the list_empty early bailout. gpu_idle isn't a
fastpath, so who cares. One candidate where we emit commands to the ring
without adding anything onto these lists is e.g. pageflip. There are
probably more.
Signed-off-by: Ben Widawsky <ben@bwidawsk.net>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Keith Packard <keithp@keithp.com>

drivers/gpu/drm/i915/i915_gem.c

@@ -2193,14 +2193,8 @@ int
 i915_gpu_idle(struct drm_device *dev)
 {
 	drm_i915_private_t *dev_priv = dev->dev_private;
-	bool lists_empty;
 	int ret, i;
 
-	lists_empty = (list_empty(&dev_priv->mm.flushing_list) &&
-		       list_empty(&dev_priv->mm.active_list));
-	if (lists_empty)
-		return 0;
-
 	/* Flush everything onto the inactive list. */
 	for (i = 0; i < I915_NUM_RINGS; i++) {
 		ret = i915_ring_idle(&dev_priv->ring[i]);