Replace some anonymous constants with PCI_ constants.

Print debugging information using aprint_debug(9) not aprint_verbose(9)
and be consistent about that.  Get rid of the pciaddrverbose switch for
debugging printfs.

Make 'static' several functions that are private to this module.

Don't test truth of arbitrary integers but compare with 0.  Change
'return (x)' to 'return x'.

(dyoung)