vfio/container: mdev cpr blocker

vfio/container: mdev cpr blocker

During CPR, after VFIO_DMA_UNMAP_FLAG_VADDR, the vaddr is temporarily
invalid, so mediated devices cannot be supported.  Add a blocker for them.
This restriction will not apply to iommufd containers when CPR is added
for them in a future patch.

Signed-off-by: Steve Sistare <steven.sistare@oracle.com>
Reviewed-by: Cédric Le Goater <clg@redhat.com>
Link: https://lore.kernel.org/qemu-devel/1749569991-25171-8-git-send-email-steven.sistare@oracle.com
[ clg: Fixed context change in VFIODevice ]
Signed-off-by: Cédric Le Goater <clg@redhat.com>