[clang] [AMDGPU] Stop coercing structs with FP and int fields to integer arrays (PR #185083)

[via cfe-commits]

addmisol wrote:

> LGTM, but I think the bitfield logic could use another round. Are we not packing if the bitfield happens to go over i32?

addressed it [here](https://github.com/llvm/llvm-project/pull/185083/changes/51246a33e1b790b81c1ecb99b521df3aae75db0e)

https://github.com/llvm/llvm-project/pull/185083