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

This patch translates Documentation/core-api/irq/index.rst into Chinese.
Signed-off-by: NYanteng Si <siyanteng@loongson.cn>
Reviewed-by: NWu XiangCheng <bobwxc@email.cn>
Link: https://lore.kernel.org/r/f6f2edfa645badfdd29122bee3ff0c9577197691.1618568135.git.siyanteng@loongson.cnSigned-off-by: NJonathan Corbet <corbet@lwn.net>

Documentation/translations/zh_CN/core-api/irq/index.rst

+.. include:: ../../disclaimer-zh_CN.rst
+
+:Original: :doc:`../../../../core-api/irq/index`
+:Translator: Yanteng Si <siyanteng@loongson.cn>
+
+.. _cn_irq_index.rst:
+
+
+====
+IRQs
+====
+
+.. toctree::
+   :maxdepth: 1
+
+   concepts
+   irq-affinity
+   irq-domain
+   irqflags-tracing