Add T=bfloat16 to custom_ops registration

[szutenberg]

Description

Brief Description of the PR:

This issue adds T=bfloat16 wherever it's relevant. The reason is that I want to add bfloat16 support of addons to my custom accelerator. It's not possible to register kernel for T=bfloat16 if op registration doesn't have it.

Type of change

• Bug fix
• New Tutorial
• Updated or additional documentation
• Additional Testing
• New Activation and the changes conform to the activation contribution guidelines
• New Callback and the changes conform to the callback contribution guidelines
• New Image addition and the changes conform to the image op contribution guidelines
• New Layer and the changes conform to the layer contribution guidelines
• New Loss and the changes conform to the loss contribution guidelines
• New Metric and the changes conform to the metric contribution guidelines
• New Optimizer and the changes conform to the optimizer contribution guidelines
• New RNN Cell and the changes conform to the rnn contribution guidelines
• New Seq2seq addition and the changes conform to the seq2seq contribution guidelines
• New Text addition and the changes conform to the text op contribution guidelines

Checklist:

• I've properly formatted my code according to the guidelines
  • By running Black + Flake8
  • By running pre-commit hooks
• This PR addresses an already submitted issue for TensorFlow Addons
• I have made corresponding changes to the documentation
• I have added tests that prove my fix is effective or that my feature works
• This PR contains modifications to C++ custom-ops

How Has This Been Tested?

build passes

[bhack]

You need to fix format.

[szutenberg]

Hi @bhack ,

I followed the instruction from STYLE_GUIDE.md. I see that there are issues with Python formatting but I didn't change any Python code.

Clang C++ code format passes.

Where do you see formatting issues?

[bhack]

Yes it Is on python and not related

[bhack]

@szutenberg Can you rebase this?