On an AS 600 5/266 (and possibly others), accessing the configuration space of PCI devices that don't exist cause PCI master & target aborts rather than returning ~0 or giving a machine check.  Bring in some code from NetBSD to handle this properly.
On an AS 600 5/266 (and possibly others), accessing the configuration
space of PCI devices that don't exist cause PCI master & target aborts
rather than returning ~0 or giving a machine check.  Bring in some code
from NetBSD to handle this properly.

obtained from:	NetBSD
reviewed by:	dfr

jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase