libstagefright: Add support for H/W AAC decoder

- Currently, only software AAC decoding is supported.
- Add support for H/W AAC decoding by including it in the
  list of available decoders and use it for decoding only
  if the property 'media.aaccodectype' is set to 0.

Change-Id: I4bb9df1bd10bd8ee91e63dadd6c473fc4e29813a
CRs-Fixed: 449145