KObj extension stage IIIb/III

KObj extension stage IIIb/III

Merge inheritance support from FreeBSD:
  * Add a simpler form of 'inheritance' for devclasses. Each devclass can
    have a parent devclass. Searches for drivers continue up the chain of
    devclasses until either a matching driver is found or a devclass is
    reached which has no parent. This can allow, for instance, pci drivers
    to match cardbus devices (assuming that cardbus declares pci as its
    parent devclass).