docs/zh_CN: add core api cpu_hotplug translation

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

Signed-off-by: Yanteng Si <siyanteng@loongson.cn>
Reviewed-by: Wu XiangCheng <bobwxc@email.cn>
Link: https://lore.kernel.org/r/5c2273563e64ccbbaf1e7ff043d2ab467879c421.1625798719.git.siyanteng@loongson.cn


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