libstagefright: support for disabling buffer metadata

- Metada mode video recording is enabled by default.
- use setprop debug.camcorder.disablemeta 1 to disable metadata mode recording.

Change-Id: I422c49c0ace0c3a3e1f4459c7e4bf29e70af763a

Conflicts:

	media/libmediaplayerservice/StagefrightRecorder.cpp