Make the FreeBSD libpciaccess routines work on FreeBSD.  The FreeBSD
sparc64 architecture needs special treatment, similar to the
PCI_MAGIC_IO_RANGE code.  However, PCI_MAGIC_IO_RANGE has been gone for
some time.  Give this a chance to work on sparc64 anyway.

This code has been in the FreeBSD ports tree for some time.