[llvm] [NVPTX] Add patterns for fma.relu.{f16|bf16} (PR #114977)

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

The tests look reasonable to me in the behaviour, but I'd prefer they `-stop-after=finalize-isel` so we can test just the isel in isolation

https://github.com/llvm/llvm-project/pull/114977