pci: remove pciutils support

We've long-since had a separation of support between pciaccess (which
is BSD-licensed) and pciutils (which is GPL-licensed).  Per #100, this
commit removes pciutils access and leaves libpciaccess support.
hwloc.doxy: update to reflect lack of pciutils support
hwloc.m4: check for libpciaccess the old-fashioned way

If we don't find libpciaccess via pkg-config, try looking the old
fashioned way, too.