[DOCS] Fix sphinx warnings

[comaniac]

Based on #4908, this is the first PR to remove all doc warnings from Python doc strings. After this fix, total number of doc warnings is reduced to 103 on my local.

[cchung100m]

Hi @comaniac

Thanks for submitting the PR.

I think that virtual_machine.rst and deploy_vision_on_vta.rst are not caught by this PR, but please correct me if I am wrong.

~/tvm/docs/contribute/pull_request.rst:33: WARNING: Unexpected indentation.
~/tvm/docs/dev/virtual_machine.rst:94: WARNING: Unexpected indentation.
~/tvm/docs/dev/virtual_machine.rst:103: WARNING: Unexpected indentation.
~/tvm/docs/dev/virtual_machine.rst:117: WARNING: Unexpected indentation.
~/tvm/docs/dev/virtual_machine.rst:130: WARNING: Unexpected indentation.
~/tvm/docs/dev/virtual_machine.rst:142: WARNING: Unexpected indentation.
~/tvm/docs/dev/virtual_machine.rst:154: WARNING: Unexpected indentation.
~/tvm/docs/dev/virtual_machine.rst:166: WARNING: Unexpected indentation.
~/tvm/docs/dev/virtual_machine.rst:179: WARNING: Unexpected indentation.
~/tvm/docs/dev/virtual_machine.rst:189: WARNING: Unexpected indentation.
~/tvm/docs/dev/virtual_machine.rst:202: WARNING: Unexpected indentation.
~/tvm/docs/dev/virtual_machine.rst:215: WARNING: Unexpected indentation.
~/tvm/docs/dev/virtual_machine.rst:223: WARNING: Unexpected indentation.
~/tvm/docs/dev/virtual_machine.rst:232: WARNING: Unexpected indentation.
~/tvm/docs/dev/virtual_machine.rst:242: WARNING: Unexpected indentation.
~/tvm/docs/dev/virtual_machine.rst:251: WARNING: Unexpected indentation.
~/tvm/docs/vta/tutorials/frontend/deploy_vision_on_vta.rst:141: WARNING: Unexpected indentation.

[comaniac]

No the warnings you listed are not covered in this PR. This PR now only covers Python files. I was planning to send another PR for RST, but I can also commit to this one if you prefer.

[tqchen]

Thanks @comaniac