docs/zh_CN: core-api: Add packing Chinese translation

Translate core-api/packing.rst into Chinese.

Last English version used:

commit 1ec779b9fabc ("docs: packing: move it to core-api book
and adjust markups").

Signed-off-by: Binbin Zhou <zhoubinbin@loongson.cn>
Reviewed-by: Wu XiangCheng <bobwxc@email.cn>
Reviewed-by: Yanteng Si<siyanteng@loongson.cn>
Reviewed-by: Alex Shi <alexs@kernel.org>
Link: https://lore.kernel.org/r/96b19575ca7e9e23941e8a5ef92120f1bffbc518.1660881950.git.zhoubinbin@loongson.cn
Signed-off-by: Jonathan Corbet <corbet@lwn.net>