drm/i915: Move retire-requests into i915_gem_wait_for_idle()

As we now distinguish everywhere that can call
i915_gem_retire_requests() following a successful wait_for_idle, we can
remove the duplication by moving that call into i915_gem_wait_for_idle()
itself.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: http://patchwork.freedesktop.org/patch/msgid/20170330145041.9005-3-chris@chris-wilson.co.uk
Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>

drivers/gpu/drm/i915/i915_debugfs.c

@@ -4179,10 +4179,6 @@ fault_irq_set(struct drm_i915_private *i915,
 	if (err)
 		goto err_unlock;
 
-	/* Retire to kick idle work */
-	i915_gem_retire_requests(i915);
-	GEM_BUG_ON(i915->gt.active_requests);
-
 	*irq = val;
 	mutex_unlock(&i915->drm.struct_mutex);
 
@@ -4286,7 +4282,7 @@ i915_drop_caches_set(void *data, u64 val)
 			goto unlock;
 	}
 
-	if (val & (DROP_RETIRE | DROP_ACTIVE))
+	if (val & DROP_RETIRE)
 		i915_gem_retire_requests(dev_priv);
 
 	lockdep_set_current_reclaim_state(GFP_KERNEL);