[llvm] [SPIRV] Add support for `bfloat16` atomics via the `SPV_INTEL_16bit_atomics` extension (PR #166257)

[Alex Voicu via llvm-commits]

AlexVlx wrote:

> FYI @vmaksimo
> 
> Lets put a link to [the spec](https://github.com/intel/llvm/pull/20009) in the description. AFAIK it's not yet final and few tokens have to be allocated.

Correct, this is only relying on the tokens that have been allocated.

https://github.com/llvm/llvm-project/pull/166257