[NVIDIA XLA] Vector BiasAdd Epilogue Fusion for FP8 GEMMs
Vector BiasAdd Epilogue Fusion for FP8 GEMMs. It's assumed that matrix bias and vector bias don't co-exist. Matrix bias fusion has been supported in [59804](https://github.com/tensorflow/tensorflow/pull/59804).  Vector bias epilog fusion is applied when beta being zero which makes matrix bias a trivial. @reedwm @philipphack 