[llvm] [LoongArch] Try to widen shuffle mask (PR #136081)

[via llvm-commits]

tangaac wrote:

Here are the files optimized by this pr:
lsx https://github.com/tangaac/loong-opt-cov-ts/commit/7b237f82a2ab8fa97548aade314e1f121a83e17e
lasx https://github.com/tangaac/loong-opt-cov-ts/commit/4c7a15c3fa65b0ff4ac45bf745b7da749cfdcd1e

https://github.com/llvm/llvm-project/pull/136081