[clang] clang/AMDGPU: Require 16-bit-insts for half typed buffer format builtins (PR #205367)

[Matt Arsenault via cfe-commits]

arsenm wrote:

Properly moving this hits a tangled mess. x86 has tests mixing the feature check, with other ABI checks that are also analyzed in codegen 

https://github.com/llvm/llvm-project/pull/205367