[llvm] RISCV: Implement isLoadFromStackSlot/isStoreToStackSlot for rvv (PR #120524)

[Matt Arsenault via llvm-commits]

https://github.com/arsenm commented:

@topperc @wangpc-pp could someone who knows about riscv pick this one up for me? 

https://github.com/llvm/llvm-project/pull/120524