docs/zh_CN: add core-api irq irq-affinity.rst translation

This patch translates Documentation/core-api/irq/irq-affinity.rst into Chinese.

Signed-off-by: Yanteng Si <siyanteng@loongson.cn>
Reviewed-by: Wu XiangCheng <bobwxc@email.cn>
Link: https://lore.kernel.org/r/d235db96434baf472441877fc8ffca0f6f70a9f5.1618568135.git.siyanteng@loongson.cn


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