docs/zh_CN: add devicetree index translation

Translate .../devicetree/index.rst into Chinese.

Signed-off-by: Yanteng Si <siyanteng@loongson.cn>
Reviewed-by: Alex Shi <alexs@kernel.org>
Link: https://lore.kernel.org/r/0a01f2eee980da02c0810d3d99b95af9013b646f.1646642188.git.siyanteng@loongson.cn


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