[clang] [llvm] [RISCV][VCIX] Add vcix_state to GNU inline assembly register set (PR #106914)

[Kito Cheng via cfe-commits]

kito-cheng wrote:

I would suggest it should prefix with a vendor prefix, either `sf.vcix_state` or `sifive.vcix_state`, also go `riscv-c-api-doc` or `riscv-toolchain-conventions` :)

https://github.com/llvm/llvm-project/pull/106914