ia64: Remove acpi_get_pxm() usage

The IOMMU, LSAPIC, IOSAPIC, and PCI host bridge code doesn't care about
_PXM values directly; it only needs to know what NUMA node the hardware is
on.

This uses acpi_get_node() directly and removes the _PXM stuff.

Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Acked-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>