Log Message:
Extend the pmf suspend/resume hooks by a shutdown method, so drivers
can register a shutdown handler explicitely.
Install a pci bus shutdown handler which disables bus master accesses
for all childs, so the drivers don't need to care.
This will hopefully be sufficient to replace the shutdownhooks
(together with the powerhooks). (It has been suggested to use some
general event notification framework for shutdown handlers, but there
might be cases where shutdown handlers must be run in an order following
the device hierarchy, which wouldn't be easy with event handlers
not tied to drivers.)
approved by David Young