vfio/pci: Introduce vfio_[attach/detach]_device

vfio/pci: Introduce vfio_[attach/detach]_device

We want the VFIO devices to be able to use two different
IOMMU backends, the legacy VFIO one and the new iommufd one.

Introduce vfio_[attach/detach]_device which aim at hiding the
underlying IOMMU backend (IOCTLs, datatypes, ...).

Once vfio_attach_device completes, the device is attached
to a security context and its fd can be used. Conversely
When vfio_detach_device completes, the device has been
detached from the security context.

At the moment only the implementation based on the legacy
container/group exists. Let's use it from the vfio-pci device.
Subsequent patches will handle other devices.

We also take benefit of this patch to properly free
vbasedev->name on failure.

Signed-off-by: Eric Auger <eric.auger@redhat.com>
Signed-off-by: Yi Liu <yi.l.liu@intel.com>
Signed-off-by: Zhenzhong Duan <zhenzhong.duan@intel.com>
Reviewed-by: Cédric Le Goater <clg@redhat.com>
Signed-off-by: Cédric Le Goater <clg@redhat.com>