vfio/common: Introduce vfio_container_init/destroy helper

vfio/common: Introduce vfio_container_init/destroy helper

This adds two helper functions vfio_container_init/destroy which will be
used by both legacy and iommufd containers to do base container specific
initialization and release.

No functional change intended.

Suggested-by: Cédric Le Goater <clg@redhat.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>