x86 / ACPI / NUMA: cleanup acpi_numa_processor_affinity_init()

Cleanup acpi_numa_processor_affinity_init() in preparation for its
move to drivers/acpi/numa.c.  It will be reused by arm64, this has no
functional change.

Signed-off-by: Hanjun Guo <hanjun.guo@linaro.org>
Signed-off-by: Robert Richter <rrichter@cavium.com>
Signed-off-by: David Daney <david.daney@cavium.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>