x86: cope with no remap space being allocated for a numa node

When allocating the pgdat's for numa nodes on x86_32 we attempt to place
them in the numa remap space for that node.  However should the node not
have any remap space allocated (such as due to having non-ram pages in
the remap location in the node) then we will incorrectly place the pgdat
at zero.  Check we have remap available, falling back to node 0 memory
where we do not.

Signed-off-by: Andy Whitcroft <apw@shadowen.org>
Acked-by: Mel Gorman <mel@csn.ul.ie>
Signed-off-by: Ingo Molnar <mingo@elte.hu>