[clang] [llvm] [AMDGPU] Add support for `v_exp_bf16` on gfx1250 (PR #149229)

[Matt Arsenault via llvm-commits]

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+; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py UTC_ARGS: --version 5
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arsenm wrote:

Can you give this a bf16 suffix instead of bfloat, and add the other targets where it's not legal 

https://github.com/llvm/llvm-project/pull/149229