DirectFB: Improve mapping of multimedia keys

The play_pause key was mapped incorrectly to direct pause. This one
maps it to togglePlayPause.

The two keys fast-forward and rewind have been mapped to
Key_AudioForward
and Key_AudioRewind, matching XCB and Android mappings.

Change-Id: I481bafab2fdfe1824b49e268e9d0754eef348cbf
Reviewed-by: Jørgen Lind <jorgen.lind@digia.com>