BathNorm tune API

[bghimireamd]

Now the priorities for find enforce are:

1. FindOptions
2. TuningPolicy (this is the new thing)
3. MIOPEN_FIND_ENFORCE value
4. defaulting to FindEnforceAction::None

This PR introduces TuningPolicy (this is the new thing)

This allows us to Tune from API.

miopenSetTuningPolicy(handle, miopenTuningPolicySearch); // set tuning miopenBatchnorm...(...); miopenSetTuningPolicy(handle, miopenTuningPolicyNone); // unset tuning

This effect is not limited to bnorm.