vfio/migration: Move migration v1 logic to vfio_migration_init()

vfio/migration: Move migration v1 logic to vfio_migration_init()

Move vfio_dev_get_region_info() logic from vfio_migration_probe() to
vfio_migration_init(). This logic is specific to v1 protocol and moving
it will make it easier to add the v2 protocol implementation later.
No functional changes intended.

Signed-off-by: Avihai Horon <avihaih@nvidia.com>
Reviewed-by: Cédric Le Goater <clg@redhat.com>
Reviewed-by: Juan Quintela <quintela@redhat.com>
Link: https://lore.kernel.org/r/20230216143630.25610-7-avihaih@nvidia.com
Signed-off-by: Alex Williamson <alex.williamson@redhat.com>