MIPS: loongson64: alloc pglist_data at run time

Loongson64 allocates arrays of pglist_data statically and is located
at Node 0, and cpu from Nodes other than 0 need remote access to
pglist_data and zone info.

Delay pglist_data allocation till run time, and make it NUMA-aware

Signed-off-by: Huang Pei <huangpei@loongson.cn>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>