drm/i915/bdw: Clean up execlist queue items in retire_work

No longer create a work item to clean each execlist queue item.
Instead, move retired execlist requests to a queue and clean up the
items during retire_requests.

v2: Fix legacy ring path broken during overzealous cleanup

v3: Update idle detection to take execlists queue into account

v4: Grab execlist lock when checking queue state

v5: Fix leaking requests by freeing in execlists_retire_requests.

Issue: VIZ-4274
Signed-off-by: Thomas Daniel <thomas.daniel@intel.com>
Reviewed-by: Deepak S <deepak.s@linux.intel.com>
Reviewed-by: Akash Goel <akash.goels@gmail.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.h b/drivers/gpu/drm/i915/intel_ringbuffer.h
index aab2e2f..8515656 100644
--- a/drivers/gpu/drm/i915/intel_ringbuffer.h
+++ b/drivers/gpu/drm/i915/intel_ringbuffer.h
@@ -236,6 +236,7 @@
 	/* Execlists */
 	spinlock_t execlist_lock;
 	struct list_head execlist_queue;
+	struct list_head execlist_retired_req_list;
 	u8 next_context_status_buffer;
 	u32             irq_keep_mask; /* bitmask for interrupts that should not be masked */
 	int		(*emit_request)(struct intel_ringbuffer *ringbuf);