message: Add Selu and Softsign to auto mixed precision gray list
  Elu and Sofplus are already part of the auto mixed precision gray list, so I think it is save to add Selu and Softsign too.
diff: @@ -129,11 +129,15 @@ class AutoMixedPrecisionLists {
  "Prod",
  "RealDiv",
  "Reciprocal",
  + "Selu",
  + "SeluGrad",
  "Sigmoid",
  "SigmoidGrad",
  "Softmax",
  "Softplus",
  "SoftplusGrad",
  + "Softsign",
  + "SoftsignGrad",
  "Sqrt",
  "Sub",
  "Tanh",
  