[llvm] [Mips] Fix atomic min/max generate mips4 instructions when compiling for mips2 (PR #159717)

[via llvm-commits]

yingopq wrote:

> > @arsenm #149983 broken atomic-min-max.ll test on the expensive builder. So I revert it and resubmit this PR, could you help review again, thanks!
> 
> What changed to fix the issue exposed by the expensive builder?

I have changed commit message, including the fix content. Thanks for your reminder.

https://github.com/llvm/llvm-project/pull/159717