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

[Mallikarjuna Gouda via cfe-commits]

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+; Test the MSA intrinsics that are encoded with the SPECIAL instruction format.
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mgoudar wrote:

I have enabled MSA feature from driver also when -mcpu i6500/i6400 is specified. Also I have added codegen test to verify MSA instructions when i650/i6400 cpu is specified. please review

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