package/on2-8170-modules: use kernel-module helper

We were already using the Linux buildsystem to build on2-8170-modules,
so just switch to the new kernel-module infra.

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Reviewed-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>