vfio: add vfio_device_prepare()

Commonize some initialization code shared by the legacy and iommufd vfio
implementations.

Reviewed-by: Cédric Le Goater <clg@redhat.com>
Signed-off-by: John Levon <john.levon@nutanix.com>
Link: https://lore.kernel.org/qemu-devel/20250507152020.1254632-2-john.levon@nutanix.com
Signed-off-by: Cédric Le Goater <clg@redhat.com>
4 files changed