vfio/common: Introduce a per container device list

vfio/common: Introduce a per container device list

Several functions need to iterate over the VFIO devices attached to
a given container.  This is currently achieved by iterating over the
groups attached to the container and then over the devices in the group.
Let's introduce a per container device list that simplifies this
search.

Per container list is used in below functions:
vfio_devices_all_dirty_tracking
vfio_devices_all_device_dirty_tracking
vfio_devices_all_running_and_mig_active
vfio_devices_dma_logging_stop
vfio_devices_dma_logging_start
vfio_devices_query_dirty_bitmap

This will also ease the migration of IOMMUFD by hiding the group
specificity.

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