vfio/igd: Handle x-igd-opregion option in config quirk

vfio/igd: Handle x-igd-opregion option in config quirk

Both enable OpRegion option (x-igd-opregion) and legacy mode require
setting up OpRegion copy for IGD devices. As the config quirk no longer
depends on legacy mode, we can now handle x-igd-opregion option there
instead of in vfio_realize.

Signed-off-by: Tomita Moeko <tomitamoeko@gmail.com>
Reviewed-by: Alex Williamson <alex.williamson@redhat.com>
Tested-by: Alex Williamson <alex.williamson@redhat.com>
Reviewed-by: Corvin Köhne <c.koehne@beckhoff.com>
Link: https://lore.kernel.org/qemu-devel/20250306180131.32970-9-tomitamoeko@gmail.com
Signed-off-by: Cédric Le Goater <clg@redhat.com>