x86-64, NUMA: Separate out numa_cleanup_meminfo()

Separate out numa_cleanup_meminfo() from numa_register_memblks().
node_possible_map initialization is moved to the top of the split
numa_register_memblks().

This patch doesn't cause behavior change.

Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Yinghai Lu <yinghai@kernel.org>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Cyrill Gorcunov <gorcunov@gmail.com>
Cc: Shaohui Zheng <shaohui.zheng@intel.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: H. Peter Anvin <hpa@linux.intel.com>