x86, ia64, acpi: Clean up x86-ism in drivers/acpi/numa.c

As pointed out by Linus CONFIG_X86 in drivers/acpi/numa.c is
ugly.

Builds and boots on ia64 (both normally and with maxcpus=8 to limit
the number of cpus).

Signed-off-by: Tony Luck <tony.luck@intel.com>
Acked-by: Yinghai Lu <yinghai@kernel.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Bjorn Helgaas <bjorn.helgaas@hp.com>
Cc: Len Brown <len.brown@intel.com>
LKML-Reference: <4D2D6B5D.4080208@kernel.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>