Add fwk_display_hwservice.

This hidl service provides information about vsync and hotplug
to vendor services which is required by at least some camera
hal implementations.

Test: VtsFwkDisplayServiceV1_0TargetTest
Test: no denials
Bug: 38311538
Change-Id: I64f0321e2832facf987057f0d48940e269d8e2d9
diff --git a/private/surfaceflinger.te b/private/surfaceflinger.te
index f04a984..3595ee4 100644
--- a/private/surfaceflinger.te
+++ b/private/surfaceflinger.te
@@ -6,6 +6,7 @@
 init_daemon_domain(surfaceflinger)
 
 typeattribute surfaceflinger mlstrustedsubject;
+typeattribute surfaceflinger display_service_server;
 
 read_runtime_log_tags(surfaceflinger)