[llvm] [RISCV] Separate doLocalPostpass into new pass and move to post vector regalloc (PR #88295)

[Luke Lau via llvm-commits]

lukel97 wrote:

> Does this change not impact `RISCV/O3-pipeline.ll` and `RISCV/O0-pipeline.ll`?

Woops yes it does, thanks, should be updated now.

https://github.com/llvm/llvm-project/pull/88295