package/hwloc: add optional dependencies to udev, libxml2, ncurses & numactl

udev:
https://github.com/open-mpi/hwloc/blob/master/config/hwloc.m4#L626

libxml2:
https://github.com/open-mpi/hwloc/blob/master/config/hwloc.m4#L1273

ncurses:
https://github.com/open-mpi/hwloc/blob/master/config/hwloc_internal.m4#L340

numactl:
https://github.com/open-mpi/hwloc/blob/master/config/hwloc_internal.m4#L419



Signed-off-by: Bernd Kuhls <bernd.kuhls@t-online.de>
[yann.morin.1998@free.fr: drop unconditional --disable-libxml2]
Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>