package/vlc: update opencv support

vlc supports both opencv-2.4 and opencv-3, so adjust the vlc package to
reflect this.

Cc: Jonathan Ben Avraham <yba@tkos.co.il>
Cc: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Samuel Martin <s.martin49@gmail.com>
Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>