[clang] [llvm] [MIPS] Add FeatureMSA to i6400 and i6500 cores (PR #134985)

[Mallikarjuna Gouda via llvm-commits]

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mgoudar wrote:

I added RUN commands for i6500/i6400 msa test to the existing test test/CodeGen/Mips/msa/arithmetic.ll and deleted new test that was added in the prev commit.

https://github.com/llvm/llvm-project/pull/134985