package/opencv: add gstreamer-1.x support

Starting with the 2.4.10 release, OpenCV supports both Gstreamer-0.10
and Gstreamer-1, but only one can be enabled at the same time (OpenCV
chooses Gstreamer-1 over Gstreamer-0.10 when both are available).

Signed-off-by: Samuel Martin <s.martin49@gmail.com>
Cc: "Yann E. MORIN" <yann.morin.1998@free.fr>
Reviewed-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>