[clang] [llvm] [RISCV] Allow `Zicsr`/`Zifencei` to duplicate with `g` (PR #136842)

[Pengcheng Wang via cfe-commits]

wangpc-pp wrote:

According to the sync-up meeting, we can proceed this patch as-is. I will merge this in a few days.

I added back the release note. @asb

https://github.com/llvm/llvm-project/pull/136842