[llvm] [Docs][RISCV]Remove experimental from Smctr, Ssctr,Sdext and Sdtrig (PR #161058)

[Shaoce SUN via llvm-commits]

sunshaoce wrote:

> Do we need to add the spec document to RISCVUsage.rst? https://github.com/riscv/riscv-debug-spec/releases https://github.com/riscv/riscv-control-transfer-records/releases/tag/v1.0_rc3

Yes, adding a `.. _riscv-debug-spec-note:` would be good. That way readers have a clear reference to the spec.

https://github.com/llvm/llvm-project/pull/161058