[clang] [CIR][AMDGPU] Use intrinsic type for dpp signature detection (PR #226921)

[Mariya Podchishchaeva via cfe-commits]

Fznamznon wrote:

> Note that this is not an RFC as it changes the signedness in parts of the builtin signatures.

Did you mean NFC?

https://github.com/llvm/llvm-project/pull/226921