x86-64, NUMA: Use common numa_nodes[]

ACPI and amd are using separate nodes[] array.  Add numa_nodes[] and
use them in all NUMA init methods.  cutoff_node() cleanup is moved
from srat_64.c to numa_64.c and applied in initmem_init() regardless
of init methods.

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>