[clang] [llvm] [RISCV] Add Smcsrind and Sscsrind extension (PR #93952)

[Craig Topper via cfe-commits]

topperc wrote:

We don't implement all the CSRs. We're missing mireg2-6, sireg2-6, and vsireg2-6

https://github.com/llvm/llvm-project/pull/93952