powerpc/pseries: Add empty update_numa_cpu_lookup_table() for NUMA=n

powerpc/pseries: Add empty update_numa_cpu_lookup_table() for NUMA=n

When CONFIG_NUMA is not set, the build fails with:

  arch/powerpc/platforms/pseries/hotplug-cpu.c:335:4:
  error: déclaration implicite de la fonction « update_numa_cpu_lookup_table »

So we have to add update_numa_cpu_lookup_table() as an empty function
when CONFIG_NUMA is not set.

Fixes: ba1c613f3fe3 ("powerpc/numa: Invalidate numa_cpu_lookup_table on cpu remove")
Signed-off-by: Corentin Labbe <clabbe@baylibre.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>