hwloc: new package

[Thomas:
  - remove mandatory libpciaccess and numactl dependencies. Those
    dependencies are optional.
  - add dependency on threads.
  - use a HWLOC_VERSION_MAJOR variable to avoid repeating the major
    version number in HWLOC_SITE.
  - explicitly disable features we don't support.
  - explicitly enable/disable pci and numa support, depending on the
    availability of the corresponding dependencies.
  - add dependency on host-pkgconf, since pkg-config can be used by
    hwloc configure script.]

Signed-off-by: Steven Noonan <steven@uplinklabs.net>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>