Add support for Tflite operator SPLIT (#3520)

Add support for Tflite operator SPLIT (#3520)

* [RFC] Initial support for Tflite operator SPLIT

This patch adds initial support for the tflite operator split. However
I am not yet sure how to handle the axis parameter for the split
operator and support it in the test infrastructure. Putting this up for
an initial review and comment.

The split operator in tflite according to
https://www.tensorflow.org/lite/guide/ops_compatibility

appears to take num_or_size_split as a 0D tensor.

I also note that tflite.split is one of the few operators that returns
multiple outputs and thus the helper routines in the tests needed some
massaging to make this work.

@apivarov , could you please review this ?

Thanks,
Ramana

* Fix the axis parameter

Add more tests

* Address review comments

* Try out frozen_gene's suggestion

* Handle split of 1 element

* int32 is only supported in tflite 1.14, let's check that version here.

* Keep this at python3.5

* Add packaging as a python package to be installed