package/opencv: reduce modules on by default

Since its integration into Buildroot, OpenCV always enables all modules
by default because the inter-module denpedency were not supported.

Now that OpenCV inter-module dependencies are correctly set at the
Buildroot configuration level, it is possible to reduce the enabled
module list to its minimal set, letting kconfig enable the other
modules.

This change will not change anything WRT a defconfig build with opencv.

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