pci_piix3_xen_ide_unplug() unplugs only disks, not CD-ROMs. It peeks
into the DriveInfo's BlockDriverState to distinguish between the two.
Unclean; use DriveInfo member media_cd, like xen_config_dev_blk().
Signed-off-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>