[llvm] [RISCV] Add support for new unprivileged extensions defined in profiles spec (PR #77458)

[Wang Pengcheng via llvm-commits]

wangpc-pp wrote:

Thanks! I was going to add them too.
These names will be used in profiles only, but I don't know if we should add them to RISCVUsage.rst.

https://github.com/llvm/llvm-project/pull/77458