[clang] [RISCV] Reduce the size of the index used for RVV intrinsics. NFC (PR #74906)

[Craig Topper via cfe-commits]

topperc wrote:

> LGTM - though maybe use uint32_t?
> 
> Looking at this code, the whole Intrinsics map vs OverloadIntrinsic map structure loops to have heavy redundancy and could be greatly simplified. Maybe a follow up?

Did you have a specific idea in mind? I'm skeptical that the `8` is the correct size for the SmallVector in OverloadedIntrinsicMap. Maybe we could use a single map and use the size of the vector being more than 1 to detect overloaded?

https://github.com/llvm/llvm-project/pull/74906