[llvm] [LoongArch] Implement LoongArchRegisterInfo::canRealignStack() (PR #76913)

[WÁNG Xuěruì via llvm-commits]

https://github.com/xen0n approved this pull request.

If it's based on some other target's similar treatment it could be useful to refer to that arch, otherwise it LGTM as-is.

https://github.com/llvm/llvm-project/pull/76913