docs/zh_CN: Update the translation of highmem to 6.1-rc8

Update to commit a9e9c939 ("Documentation/mm: add
details about kmap_local_page() and preemption").

Commit 84b86f60 ("Documentation/mm: rrefer
kmap_local_page() and avoid kmap()").
Commit 6b3afe2e ("Documentation/mm: avoid
invalid use of addresses from kmap_local_page()").
Commit 516ea046 ("Documentation/mm: don't kmap*()
pages which can't come from HIGHMEM").

Signed-off-by: Yanteng Si <siyanteng@loongson.cn>
Reviewed-by: Wu XiangCheng <bobwxc@email.cn>
Link: https://lore.kernel.org/r/50db59505546b035a03f4ae48d3c18e6116f9e3c.1670642548.git.siyanteng@loongson.cn


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