Add SELinux properties for artd

Test: boot device and check for artd process
Change-Id: I2a161701102ecbde3e293af0346d1db0b11d4aab
diff --git a/private/service_contexts b/private/service_contexts
index c9c6aef..3357943 100644
--- a/private/service_contexts
+++ b/private/service_contexts
@@ -51,6 +51,7 @@
 gsiservice                                u:object_r:gsi_service:s0
 appops                                    u:object_r:appops_service:s0
 appwidget                                 u:object_r:appwidget_service:s0
+artd                                      u:object_r:artd_service:s0
 assetatlas                                u:object_r:assetatlas_service:s0
 attention                                 u:object_r:attention_service:s0
 audio                                     u:object_r:audio_service:s0