Move the generic 64bit NUMA init machinery from numa_64.c to numa.c.

* node_data[], numa_mem_info and numa_distance
* numa_add_memblk[_to](), numa_remove_memblk[_from]()
* numa_set_distance() and friends
* numa_init() and all the numa_meminfo handling helpers called from it
* dummy_numa_init()
* memory_add_physaddr_to_nid()

A new function x86_numa_init() is added and the content of
numa_64.c::initmem_init() is moved into it.  initmem_init() now simply
calls x86_numa_init().

Constants and numa_off declaration are moved from numa_{32|64}.h to
numa.h.

This is code reorganization and doesn't involve any functional change.
Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Yinghai Lu <yinghai@kernel.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: "H. Peter Anvin" <hpa@zytor.com>