drm/radeon/kms: use wait queue (events) for VBLANK sync

This already simplifies code significally and makes it maintaible
in case of adding memory reclocking plus voltage changing in future.

Signed-off-by: Rafał Miłecki <zajec5@gmail.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>

drivers/gpu/drm/radeon/radeon_device.c

@@ -645,6 +645,7 @@ int radeon_device_init(struct radeon_device *rdev,
 	mutex_init(&rdev->pm.mutex);
 	rwlock_init(&rdev->fence_drv.lock);
 	INIT_LIST_HEAD(&rdev->gem.objects);
+	init_waitqueue_head(&rdev->irq.vblank_queue);
 
 	/* setup workqueue */
 	rdev->wq = create_workqueue("radeon");