qdev-monitor: add missing aliases for virtio device classes

qdev-monitor: add missing aliases for virtio device classes

virtio-{blk,balloon,net,serial} are aliases for their actual,
architecture-dependent implementations (*-ccw on s390x, *-pci on other
architectures supporting virtio). This makes it a lot easier to craft
qemu invocations that work on all supported architectures. Complete
the set to cover all existing non-abstract virtio device classes.

For virtio-balloon, only the CCW implementation was missing.

Signed-off-by: Sascha Silbe <[email protected]>
Message-Id: <1455831854[email protected]>
Reviewed-by: Cornelia Huck <[email protected]>
Reviewed-by: Michael S. Tsirkin <[email protected]>
Signed-off-by: Markus Armbruster <[email protected]>