qdev: replace bus_type enum with bus_info struct.

BusInfo is filled with name and size (pretty much like I did for
DeviceInfo as well).  There is also a function pointer to print
bus-specific device information to the monitor.  sysbus is hooked
up there, I've also added a print function for PCI.

Device creation is slightly modified as well:  The device type search
loop now also checks the bus type while scanning the list instead of
complaining thereafter in case of a mismatch.  This effectively gives
each bus a private namespace for device names.

Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
Signed-off-by: Paul Brook <paul@codesourcery.com>
