Revert "drm/i915: Drop ring->lazy_request"

With multiple rings generating requests independently, the outstanding
requests must also be track independently.

Reported-by: Wang Jinjin <jinjin.wang@intel.com>
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=30380
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>

drivers/gpu/drm/i915/intel_ringbuffer.h

@@ -81,6 +81,11 @@ struct  intel_ring_buffer {
 	 */
 	struct list_head request_list;
 
+	/**
+	 * Do we have some not yet emitted requests outstanding?
+	 */
+	bool outstanding_lazy_request;
+
 	wait_queue_head_t irq_queue;
 	drm_local_map_t map;
 };