[llvm] [MIPS] Add Scheduling model for MIPS i6400 and i6500 CPUs (PR #132704)

[Min-Yih Hsu via llvm-commits]

https://github.com/mshockwave approved this pull request.

Personally I'm not really a fan of using InstRW as I pointed out in one of my comments. But I guess it's up to MIPS maintainers to make the call on that. Other than that, LGTM.
@djtodoro do you have any other comments?

https://github.com/llvm/llvm-project/pull/132704