[llvm] [RISCV][CG]Use processShuffleMasks for per-register shuffles (PR #120803)

[Alexey Bataev via llvm-commits]

alexey-bataev wrote:

> Hm, noticed the usual auto update on the review didn't happen for some reason. I have revered this in commit [6840521](https://github.com/llvm/llvm-project/commit/684052173971868aab0e6b62d7770a6299e84141) for the reason described in the revert commit.

Unable to reproduce a crash, need a reproducer

https://github.com/llvm/llvm-project/pull/120803