[llvm] [Mips] Print ABI register names in MIR (PR #228017)

[Matt Arsenault via llvm-commits]

https://github.com/arsenm requested changes to this pull request.

The MIR register names must exactly match tablegen the tablegen records, and no aliases. I do not want to have to know additional MIPS specific context to understand a testcase 

https://github.com/llvm/llvm-project/pull/228017