[llvm] [RISCV] Add groupid/bitmask for RISC-V extension (PR #94440)

[Piyou Chen via llvm-commits]

BeMg wrote:

Align the bitmask with https://github.com/riscv-non-isa/riscv-c-api-doc/pull/74.

https://github.com/llvm/llvm-project/pull/94440