qdev: create default bus names.

qdev: create default bus names.

Create a default bus name if none is passed to qbus_create().

If the parent device has DeviceState->id set it will be used to create
the bus name,. i.e. -device lsi,id=foo will give you a scsi bus named
"foo.0".

If there is no id BusInfo->name (lowercased) will be used instead, i.e.
-device lsi will give you a scsi bus named "scsi.0".

A scsi adapter with two scsi busses would have "scsi.0" and "scsi.1" or
"$id.0" and "$id.1" busses.  The numbers of the child busses are per
device, i.e. when adding two lsi adapters both will have a "*.0" child
bus.

Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>