libstagefright: Add hooks for extended media utils

Add following enhancements:
 - Shell property to disable audio
   property: persist.debug.sf.noaudio
   0 = all audio enabled
   1 = audio decode disabled (AwesomePlayer)
   2 = audio encode disabled (StagefrightRecorder)
   3 = audio encode & decode disabled
 - Shell property to override encoding profiles
   property: encoder.video.profile
   H264 profiles: base, main, high
   MPEG4 profiles: simple, asp

CRs: 573176

Change-Id: Iec32177cae40b0de606b52bbbd41eb24b1643c56