docs/zh_CN: add core-api symbol-namespaces.rst translation

Translates Documentation/core-api/symbol-namespaces.rst into Chinese.

Signed-off-by: Yanteng Si <siyanteng@loongson.cn>
Reviewed-by: Wu XiangCheng <bobwxc@email.cn>
Link: https://lore.kernel.org/r/20210527064347.3936694-1-siyanteng@loongson.cn


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