libstagefright: support for disabling buffer metadata

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

Ported from jellybean (was Change-Id: I8ce90e633b262c5b2d1c9d7e367b7b5487b6d1b4)

http://review.cyanogenmod.org/#/c/22404/

Signed-off-by: Michael Bestas <mikeioannina@gmail.com>

Change-Id: I422c49c0ace0c3a3e1f4459c7e4bf29e70af763a