package/igh-ethercat: use kernel-module helper

igh-ethercat's Makefile just contains calls to the Linux buildsystem,
that do exactly what we now do with our 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>