[xla] Add debug option flag xla_use_shardonnay.
[xla] Add debug option flag xla_use_shardonnay.

FUTURE_COPYBARA_INTEGRATE_REVIEW=https://github.com/openxla/xla/pull/12537 from Intel-tensorflow:sachin/softmax-axis de9d6bd36272962faf76077f594649d229bb727a
