Allow PCI config space syscalls to be used by 64-bit processes.

The pciconfig_iobase, pciconfig_read and pciconfig_write system calls
were only implemented for 32-bit processes; for 64-bit processes they
returned an ENOSYS error.  This allows them to be used by 64-bit
processes as well.  The X server uses pciconfig_iobase at least, and
this change is necessary to allow a 64-bit X server to work on my G5.

Signed-off-by: Paul Mackerras <paulus@samba.org>