[llvm] [MIPS][float] Fixed SingleFloat codegen on N32/N64 targets (PR #140575)

[Davide Mor via llvm-commits]

Tazdevil971 wrote:

Ping @arsenm.

Recap:
- I've added missing test cases and renamed existing ones
- I haven't touched the existing tests as that is still an open question, [here](https://github.com/llvm/llvm-project/blob/8fda8677250b1bb1d3fc476deb8329c55c8b3942/llvm/test/CodeGen/Mips/cconv/arguments-float.ll) I tried doing it. If you think it looks better that way I can do it on all of them and add it to the PR.

https://github.com/llvm/llvm-project/pull/140575