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

[Kito Cheng via cfe-commits]

kito-cheng wrote:

> Do you mean change the current vcix_state register to sf.vcix_state?

Yes, because it's SiFive specific register, other vendor may add other status register like VCIX in future, so I would like to add prefix to make sure all further similar stuff will follow same rule if possible 

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