allow mediatranscoding service to be stack dumped

bug: 170975812
Change-Id: Id73aaf5343efa3c67470e51f63a663a1684e7bf6
diff --git a/private/system_server.te b/private/system_server.te
index a3ee549..48c884c 100644
--- a/private/system_server.te
+++ b/private/system_server.te
@@ -289,6 +289,7 @@
   mediametrics
   mediaserver
   mediaswcodec
+  mediatranscoding
   netd
   sdcardd
   statsd