libstagefright: Add support for High Frame Rate Encoding

- Based on kkeyhfr key value from meta data, add support in OMXCodec and
  MPEG4Writer for HFR mode
- Assume normal mode recording if kKeyHfr is absent
- Increase bit rate for high frame rate (HFR) recording feature to reflect
  the corresponding increase in frame rate

Change-Id: I0a69f8d9322a768677781d08dd910dc5772c5292