trancoding: lazy-start transcoding service

bug: 186387244
test: atest MediaTranscodeManagerTest; unit tests
Change-Id: I80bb476abf919b908ac9b79c32b09bdc90876cf0
diff --git a/apex/mediatranscoding.rc b/apex/mediatranscoding.rc
index 24306a2..ae9f8ba 100644
--- a/apex/mediatranscoding.rc
+++ b/apex/mediatranscoding.rc
@@ -8,4 +8,5 @@
     ioprio rt 4
     # Restrict to little cores only with system-background cpuset.
     writepid /dev/cpuset/system-background/tasks
+    interface aidl media.transcoding
     disabled