vfio/igd: Move LPC bridge initialization to a separate function

vfio/igd: Move LPC bridge initialization to a separate function

A new option will soon be introduced to decouple the LPC bridge/Host
bridge ID quirk from legacy mode. To prepare for this, move the LPC
bridge initialization into a separate function.

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/20250306180131.32970-5-tomitamoeko@gmail.com
Signed-off-by: Cédric Le Goater <clg@redhat.com>