MediaTranscodingService: Add sepolicy for MediaTranscodingService.

Bug:145233472
Test: Build and flash the phone.
"adb shell dumpsys -l | grep media" shows media.transcoding service.

Change-Id: I48a42e7b595754989c92a8469eb91360ab6db7c6
diff --git a/private/service_contexts b/private/service_contexts
index fa52a05..1902a48 100644
--- a/private/service_contexts
+++ b/private/service_contexts
@@ -118,6 +118,7 @@
 media.player                              u:object_r:mediaserver_service:s0
 media.metrics                             u:object_r:mediametrics_service:s0
 media.extractor                           u:object_r:mediaextractor_service:s0
+media.transcoding                         u:object_r:mediatranscoding_service:s0
 media.resource_manager                    u:object_r:mediaserver_service:s0
 media.sound_trigger_hw                    u:object_r:audioserver_service:s0
 media.drm                                 u:object_r:mediadrmserver_service:s0