Documentation: Chinese translation of arm64/legacy_instructions.txt

This is a Chinese translated version of
Documentation/arm64/legacy_instructions.txt

It is based on the modifications of
Documentation/arm64/legacy_instructions.txt in submission: "587064b6",
"bd35a4ad", "2d888f48", "c852f320".

Signed-off-by: Fu Wei <wefu@redhat.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>