Let's introduce two helpers that allow to DMA map/unmap a RAM
section. Those helpers will be called for nested stage setup in
another call site. Also the vfio_listener_region_add/del()
structure may be clearer.
Signed-off-by: Eric Auger <eric.auger@redhat.com>
Signed-off-by: Kunkun Jiang <jiangkunkun@huawei.com>
