This commit is currently implementing supports for scalar cryptography extension for LLVM according to version 0.9.0 (Pre-release) and version 0.8.1 of [K Ext specification](https://github.com/riscv/riscv-crypto/releases). Currently, we are implementing the MC (Machine Code) layer of his extension and the majority of work is done under `llvm/lib/Target/RISCV` directory. There are also some test files in `llvm/test/MC/RISCV/rvk` directory.
Add two new CSR, `MNOISE` and `MENTROPY`.
Add two new Immediate numbers, `uimm2` and `rcon`.
//**Recognising that it might be better to add the definition of the immediate number `uimm2` into file `RISCVInstrInfo.td`, we will update diff soon**//
**Co-author：**@ksyx & @VincentWu