ACPI / NUMA: move acpi_numa_slit_init() to drivers/acpi/numa.c

Identical implementations of acpi_numa_slit_init() are used by both
x86 and follow-on arm64 support.  Move it to drivers/acpi/numa.c, and
guard with CONFIG_X86 || CONFIG_ARM64 because ia64 has its own
architecture specific implementation.

No code 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>