ACPI/NUMA: Do not map pxm to node when NUMA is turned off

acpi_map_pxm_to_node() unconditially maps nodes even when NUMA is turned
off. So acpi_get_node() might return a node > 0, which is fatal when NUMA
is disabled as the rest of the kernel assumes that only node 0 exists.

Expose numa_off to the acpi code and return NUMA_NO_NODE when it's set.

Signed-off-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Cc: fenghua.yu@intel.com
Cc: tony.luck@intel.com
Cc: linux-ia64@vger.kernel.org
Cc: catalin.marinas@arm.com
Cc: rjw@rjwysocki.net
Cc: will.deacon@arm.com
Cc: linux-acpi@vger.kernel.org
Cc: linux-arm-kernel@lists.infradead.org
Cc: lenb@kernel.org
Link: http://lkml.kernel.org/r/1481602709-18260-1-git-send-email-boris.ostrovsky@oracle.com
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>