stagefright: Support hardware codecs with FFMPEG extractor

 * Quite often we'll be using our custom extractor to handle
   container formats which aren't supported by any other means,
   but the codecs used inside the container are hardware supported.
 * For QC specifically we need to send a few magical incantations,
   so add support for this. Software codecs will be used if
   hardware support is unavailable.

Change-Id: I917b674142fdab0b009e066e9511648c2695ec4b