pds_vdpa: get vdpa management info

Find the vDPA management information from the DSC in order to
advertise it to the vdpa subsystem.

Signed-off-by: Shannon Nelson <shannon.nelson@amd.com>
Acked-by: Jason Wang <jasowang@redhat.com>
Message-Id: <20230519215632.12343-7-shannon.nelson@amd.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>