ACPI: Add out of bounds and numa_off protections to pxm_to_node()

The function should check the validity of the pxm value before using
it to index the pxm_to_node_map[] array.

Whilst hardening this code may be good in general, the main intent
here is to enable following patches that use this function to replace
acpi_map_pxm_to_node() for non SRAT usecases which should return
NO_NUMA_NODE for PXM entries not matching with those in SRAT.

Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Reviewed-by: Barry Song <song.bao.hua@hisilicon.com>
Reviewed-by: Hanjun Guo <guohanjun@huawei.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>