docs/zh_CN: add core api memory_hotplug translation

Translate Documentation/core-api/memory_hotplug.rst into Chinese.

Signed-off-by: Yanteng Si <siyanteng@loongson.cn>
Reviewed-by: Wu XiangCheng <bobwxc@email.cn>
Reviewed-by: Alex Shi <alexs@kernel.org>
Link: https://lore.kernel.org/r/55a74c9fe5627edff36fa01940eae943f0861f8e.1625797729.git.siyanteng@loongson.cn


Signed-off-by: Jonathan Corbet <corbet@lwn.net>