[clang] [llvm] [RISCV][LLVM][Clang] Add experimental `Zvvm` config intrinsics (PR #203774)

[via cfe-commits]

imkiva wrote:

The upstream IME spec has changed 2 days ago. They are currently reviewing these three configuration intrinsics.

`__riscv_ime_lambda()` is now the pure selected-lambda query, and `__riscv_vsetlambda(0)` is no longer read-only -- it is a preserve-or-initialize write request. 
I will remove `__riscv_vsetlambda` in this PR until it has a stable explanation, only keep two read-only query intrinsics for now.

https://github.com/llvm/llvm-project/pull/203774