[llvm] [MIPS] Fix missing ANDI optimization (PR #97689)

[via llvm-commits]

yingopq wrote:

> I don't work on MIPS anymore but this looks correct to me.
> 
> One nit: I think it would be good to pre-commit the test with the existing codegen first and then have this patch show the codegen improvement.

Yes, this would be best. Thanks! 
Need I split it into two patches and resubmit again?

https://github.com/llvm/llvm-project/pull/97689