[llvm] [CodeGen][RISCV] Add [u]int{64, 128} to bf16 libcalls (PR #70933)

[Phoebe Wang via llvm-commits]

https://github.com/phoebewang approved this pull request.

The names look good to me.
I know nothing about RISCV instrcutions, need one more look from RISCV experts.

https://github.com/llvm/llvm-project/pull/70933