[llvm] [RISCV] Use QC_E_ADDI while eliminating the frameindex (PR #139515)

[Sam Elliott via llvm-commits]

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

LGTM. 

If SrcReg and DestReg are the same you could also use `qc.e.addai` but I think stack frames larger than 2^25 bytes are unlikely, so we can probably skip that.

https://github.com/llvm/llvm-project/pull/139515