x86-64, numa: Allocate memnodemap under max_pfn_mapped

We need to access it right way, so make sure that it is mapped already.

Prepare to put page table on local node, and nodemap is used before that.

Signed-off-by: Yinghai Lu <yinghai@kernel.org>
LKML-Reference: <4D1933C8.7060105@kernel.org>
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>