[llvm] [NVPTX] Add patterns for fma.relu.{f16|f16x2|bf16|bf16x2} (PR #114977)

[Hugh Delaney via llvm-commits]

hdelan wrote:

FTZ FMA is not supported for bf16, so I have removed some patterns elsewhere that were allowing `fma.rn.ftz.bf16` to be emitted.

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