[llvm] [LoongArch] Improve codegen for atomic ops (PR #67391)

[Lu Weining via llvm-commits]

SixWeining wrote:

It's better to create 2 seperate PRs for each commit. Refer: https://llvm.org/docs/GitHub.html#creating-pull-requests

https://github.com/llvm/llvm-project/pull/67391