[llvm] [RISCV] Add DAG combine for forming VAADDU_VL from VP intrinsics. (PR #124848)

[Luke Lau via llvm-commits]

https://github.com/lukel97 approved this pull request.

LGTM

Could we also do this after legalization and try and match it on `TRUNCATE_VECTOR_VL`? That way we would also match fixed length vectors.

https://github.com/llvm/llvm-project/pull/124848