x86: unify 64-bit UMA and NUMA paging_init()

64-bit UMA and NUMA versions of paging_init() are almost identical.
Therefore, merge the copy in mm/numa_64.c to mm/init_64.c to remove
duplicate code.

[ Impact: cleanup ]

Signed-off-by: Pekka Enberg <penberg@cs.helsinki.fi>
LKML-Reference: <1241699741.17846.30.camel@penberg-laptop>
Signed-off-by: Ingo Molnar <mingo@elte.hu>