[clang] [llvm] [RISCV] Support Base P RV32/64 Instructions (PR #150379)

[via llvm-commits]

realqhc wrote:

I am seeking to receive review and comments on naming scheme for the tablegen classes, like `RVPShiftN_ri` and `RVPBinaryScalar_rr`. Any suggesion would be highly valuable. Thank you. 

https://github.com/llvm/llvm-project/pull/150379