Add imms service and system_app_service type.

Map imms to system_app_service in service_contexts and add
the system_app_service type and allow system_app to add the
system_app_service.

Bug: 16005467
Change-Id: I06ca75e2602f083297ed44960767df2e78991140
diff --git a/service_contexts b/service_contexts
index 843d6ac..0f4212b 100644
--- a/service_contexts
+++ b/service_contexts
@@ -46,6 +46,7 @@
 iphonesubinfo2                            u:object_r:radio_service:s0
 iphonesubinfo                             u:object_r:radio_service:s0
 ims                                       u:object_r:radio_service:s0
+imms                                      u:object_r:system_app_service:s0
 isms_msim                                 u:object_r:radio_service:s0
 isms2                                     u:object_r:radio_service:s0
 isms                                      u:object_r:radio_service:s0