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

[Alexander Richardson via llvm-commits]

arichardson 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?
> > 
> > 
> > You could commit the baseline test directly and then just update this pull request.
> 
> OK, I submitted test #102278. Please help review, thanks!

I've merged that other commit, once this one has been rebased I can go ahead and merge it. Thanks!

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