Add a new `CreateIntrinsic` overload with no `Types`, useful for creating calls to non-overloaded intrinsics that don't need additional mangling.
- Move all HLSL code out of AMDGPU.cpp to CGHLSLBuiltins.cpp - Fixes accidental reorganization of HLSL code into AMDGPU caused by (https://github.com/llvm/llvm-project/pull/132252, https://github.com/llvm/llvm-project/commit/7f920e2e5f70b)