docs/zh_CN: add free_page_reporting translation

Translate .../vm/free_page_reporting.rst into Chinese.

Signed-off-by: Yanteng Si <siyanteng@loongson.cn>
Reviewed-by: Alex Shi <alexs@kernel.org>
Link: https://lore.kernel.org/r/4ef77c1be8319fc45b18e9f4c41986095d794562.1643246827.git.siyanteng@loongson.cn


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