[llvm] [RISCV][CFI] add function epilogue cfi information (PR #110810)

[Sam Elliott via llvm-commits]

lenary wrote:

Sorry, those three comments were supposed to come together, like a review. Hopefully they are helpful though. Please test looking at the `frame variable` information (or equivalent in LLDB) at all instruction boundaries in the epilog.

https://github.com/llvm/llvm-project/pull/110810