[clang] [llvm] [RISCV] Make zvknha a subset of zvknhb (PR #178680)

[Nicolas Brunie via cfe-commits]

nibrunieAtSi5 wrote:

After discussion with a few knowledgeable folks at RVIA, I have open a PR to clarify this in the **vector-cryto** https://github.com/riscv/riscv-isa-manual/pull/2635.
The suggestion is to make it explicit that **Zvknhb** implies **Zvknha**.

Thank you @4vtomat for bringing this to my attention.

https://github.com/llvm/llvm-project/pull/178680