[llvm] [RISCV] Add a rematerializable pseudo instruction for LUI+ADDI for global addresses. (PR #93352)

[Philip Reames via llvm-commits]

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

LGTM w/minor comment.

Note - I see this as mostly a stepping stone and a way to make forward progress.  If we want to keep discussing removing the one use in favor of https://github.com/llvm/llvm-project/pull/93142, I'm happy to keep doing so.

https://github.com/llvm/llvm-project/pull/93352