drm: update drm_show_memory_stats() for dma-bufs

Show buffers as shared if they are shared via dma-buf as well
(e.g., shared with v4l or some other subsystem).

v2: switch to gem helper

Link: https://lore.kernel.org/all/[e-mail]/
Reviewed-by: Rob Clark <[e-mail]> (v1)
Reviewed-by: Tvrtko Ursulin <[e-mail]>
Signed-off-by: Alex Deucher <[e-mail]>
Reviewed-by: Christian König <[e-mail]>
Signed-off-by: Christian König <[e-mail]>

drivers/gpu/drm/drm_file.c

···
 					DRM_GEM_OBJECT_PURGEABLE;
 		}
 
-		if (obj->handle_count > 1) {
+		if (drm_gem_object_is_shared_for_memory_stats(obj)) {
 			status.shared += obj->size;
 		} else {
 			status.private += obj->size;