conf: introduce support for firmware auto-selection feature filtering

conf: introduce support for firmware auto-selection feature filtering

When the firmware auto-selection was introduced it always picked first
usable firmware based on the JSON descriptions on the host. It is
possible to add/remove/change the JSON files but it will always be for
the whole host.

This patch introduces support for configuring the auto-selection per VM
by adding users an option to limit what features they would like to have
available in the firmware.

Signed-off-by: Pavel Hrdina <phrdina@redhat.com>
Reviewed-by: Michal Privoznik <mprivozn@redhat.com>