[llvm] AMDGPU: Use OtherPredicates for v_dot2_bf16_bf16(f16_f16) pseudo (PR #84354)

[Changpeng Fang via llvm-commits]

changpeng wrote:

> LGTM, but this is really unfortunate. Can we try to address dpp predicates?


let SubtargetPredicate = HasDPP8;

I am thinking whether we can put hasDPP8 into OtherPredicates (using concat). But we need to be
very careful of the ordering this assignment with copy from pseudo to real of OtherPredicates. 

https://github.com/llvm/llvm-project/pull/84354