x86-64, NUMA: Trivial changes to prepare for emulation updates

* Separate out numa_add_memblk_to() from numa_add_memblk() so that
  different numa_meminfo can be used.

* Rename cmdline to emu_cmdline.

* Drop @start/last_pfn from numa_emulation() and use max_pfn directly.

This patch doesn't introduce any 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>