[llvm] [AMDGPU][GlobalISel] Allow bitcast of bf16 (PR #81674)

[Stanislav Mekhanoshin via llvm-commits]

https://github.com/rampitec commented:

It is there for a reason. You cannot really enable it without implementing global isel support for bf16. It will start failing silently. The point of this code to fail with an error. It will also start silently failing for multiple targets.

https://github.com/llvm/llvm-project/pull/81674