package/kmod: add option for host variant

package/kmod: add option for host variant

Curently, host-kmod has no option to enable it, because only
the kernel depends on it, and this is unconditional (because
we can't know if modules will be enabled in the kernel config).

But we're soon to add options to enable various features of
kmod, so we'll need a place where to show those features.

Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>
Cc: Yegor Yefremov <yegorslists@googlemail.com>
Cc: Lucian Buga <lucianbuga@gmail.com>
Tested-by: Matt Weber <matthew.weber@rockwellcollins.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>