[llvm] [Mips] Fix atomic min/max generate mips4 instructions when compiling for mips2 (PR #149983)

[via llvm-commits]

yingopq wrote:

> Is there a reason mips is reinventing all this stuff in a machine pass? AtomicExpand should already handle all of this?

Sorry, I did not find this reason.

https://github.com/llvm/llvm-project/pull/149983