vfio/container: Introduce vfio_address_space_insert()

vfio/container: Introduce vfio_address_space_insert()

It prepares ground for a future change initializing the 'space' pointer
of VFIOContainerBase. The goal is to replace vfio_container_init() by
an .instance_init() handler when VFIOContainerBase is QOMified.

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