stagefright: add support for output frame rendered callback

- Added FRAME_RENDERED event in OMX, used by tunneled video decoders
  to signal rendered event timing
- Track buffers sent for rendering in ACodec and in SoftwareRenderer, and
  determine when they have rendered
- Propagate render times to MediaCodec

Bug: 20503131
Change-Id: Idf0a8714d5368b237c2285dd39fa82db847c232f