vfio/container: preserve descriptors

vfio/container: preserve descriptors

At vfio creation time, save the value of vfio container, group, and device
descriptors in CPR state.  On qemu restart, vfio_realize() finds and uses
the saved descriptors.

During reuse, device and iommu state is already configured, so operations
in vfio_realize that would modify the configuration, such as vfio ioctl's,
are skipped.  The result is that vfio_realize constructs qemu data
structures that reflect the current state of the device.

Signed-off-by: Steve Sistare <steven.sistare@oracle.com>
Reviewed-by: Cédric Le Goater <clg@redhat.com>
Reviewed-by: Zhenzhong Duan <zhenzhong.duan@intel.com>
Link: https://lore.kernel.org/qemu-devel/1749569991-25171-5-git-send-email-steven.sistare@oracle.com
Signed-off-by: Cédric Le Goater <clg@redhat.com>