Add audio tag to systrace

Change-Id: I0e39443eec7420b21827d3255b985028fee09b92
diff --git a/systrace.py b/systrace.py
index 2358569..232aca3 100755
--- a/systrace.py
+++ b/systrace.py
@@ -21,6 +21,7 @@
   'wm':       1<<5,
   'am':       1<<6,
   'sync':     1<<7,
+  'audio':    1<<8,
 }
 
 def main():