This assumes ide-drive.wwn, ide-hd.wwn, ide-cd.wwn were supported
at the same time, similar for scsi-disk.wwn, scsi-hd.wwn, and
scsi-cd.wwn. So only two new caps (QEMU_CAPS_IDE_DRIVE_WWN,
and QEMU_CAPS_SCSI_DISK_WWN) are introduced.