[packages] mpd: enable opus support

Signed-off-by: Dirk Neukirchen <dirkneukirchen@web.de>
[packages] import libmad

Signed-off-by: Dirk Neukirchen <dirkneukirchen@web.de>
[packages] mpd: add libmad

Signed-off-by: Dirk Neukirchen <dirkneukirchen@web.de>