[llvm] [RISCV] Use addi rather than addiw for immediates materialised by lui+addi(w) pairs when possible (PR #141663)

[Philip Reames via llvm-commits]

https://github.com/preames commented:

Just noting that I like the direction here, but am deferring the review to Craig as he's better at this type of stuff than I am.  

https://github.com/llvm/llvm-project/pull/141663