PlaybackService: send EFFECT_CONTROL_SESSION on media state update

Send the *_EFFECT_CONTROL_SESSION intent when the state of current media
is updated. It allows external audio effects like equalizer or
visualizer to know the audio session id used by VLC and apply their own
effect.
See android.media.audiofx.AudioEffect.

Signed-off-by: Geoffrey Métais <geoffrey.metais@gmail.com>
(cherry picked from commit 00316e7f)