qdev: Convert busses to QEMU Object Model

This is far less interesting than it sounds.  We simply add an Object to each
BusState and then register the types appropriately.  Most of the interesting
refactoring will follow in the next patches.

Since we're changing fundamental type names (BusInfo -> BusClass), it all needs
to convert at once.  Fortunately, not a lot of code is affected.

Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
[AF: Made all new bus TypeInfos static const.]
[AF: Made qbus_free() call object_delete(), required {qom,glib}_allocated]
Signed-off-by: Andreas Färber <afaerber@suse.de>