ACPI: remove NID_INVAL

NUMA_NO_NODE has been exported globally and thus it can replace NID_INVAL
in the acpi code.

Also removes the unused acpi_unmap_pxm_to_node() function.

[akpm@linux-foundation.org: coding-style fixes]
Cc: Cyrill Gorcunov <gorcunov@openvz.org>
Cc: Lee Schermerhorn <Lee.Schermerhorn@hp.com>
Reviewed-by: Christoph Lameter <cl@linux-foundation.org>
Signed-off-by: David Rientjes <rientjes@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Len Brown <len.brown@intel.com>