ACPI/NUMA: Remove architecture dependent remainings

With the removal of the Itanium architecture [1] the last architecture
dependent functions:

 acpi_numa_slit_init(), acpi_numa_memory_affinity_init()

were removed. Remove its remainings in the header files too and make
them static.

[1] commit cf8e8658 ("arch: Remove Itanium (IA-64) architecture")

Reviewed-by: Dan Williams <dan.j.williams@intel.com>
Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Reviewed-by: Alison Schofield <alison.schofield@intel.com>
Signed-off-by: Robert Richter <rrichter@amd.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>