add PT softmax ops to the benchmark suite (#21208)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/21208
The diff adds softmax, softmax2d, and logsoftmax to the benchmark suite.
Reviewed By: zheng-xq
Differential Revision: D15526265
fbshipit-source-id: b7ba63032dba7146765513c8cb1ac5a6a7bd1a68
