Tensorflow frontend - Softmax

Currently, a TF softmax op gets mapped to NNVM “Flatten + Softmax” symbol.

@srkreddy1238

I see that softmax now supports axis. So, is flatten symbol still required? If not, I can work on it and send a PR.

I think ‘take’ op is similar here

@janimesh yes, the extra fixes not needed now.
Please send a PR and also add a test case for the same. Thanks.