the current cross_entropy_op does not support soft label.

[lcy-seso]

The current cross_entropy_op does not consider when a soft label is given rather than a hard label. This is not enough.

Here is the example in caffe2: https://github.com/caffe2/caffe2/blob/master/caffe2/operators/cross_entropy_op.cc#L200, and TF also supports the cross entropy with soft label.