yolov3 training on IPU

[HuDi2018]

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[ZwwWayne]

Hi @HuDi2018

Thanks for your kind PR. It seems that CLA is not signed. Could you sign the CLA so that eventually we could merge this PR after review? You can check the contents and follow the instruction in the communication box shown as below

[codecov]

Codecov Report

Attention: 288 lines in your changes are missing coverage. Please review.

Comparison is base (3b72b12) 64.17% compared to head (26476e9) 63.53%.
Report is 96 commits behind head on dev.

Files	Patch %	Lines
mmdet/models/dense_heads/yolo_head_ipu.py	11.45%	115 Missing and 1 partial ⚠️
mmdet/datasets/pipelines/ipu_pipelines.py	23.80%	80 Missing ⚠️
mmdet/models/backbones/darknet_ipu.py	16.07%	46 Missing and 1 partial ⚠️
mmdet/apis/test.py	5.00%	38 Missing ⚠️
mmdet/apis/train.py	0.00%	5 Missing ⚠️
mmdet/models/detectors/single_stage.py	60.00%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##              dev    #8552      +/-   ##
==========================================
- Coverage   64.17%   63.53%   -0.64%     
==========================================
  Files         361      364       +3     
  Lines       29530    29881     +351     
  Branches     5020     5079      +59     
==========================================
+ Hits        18951    18986      +35     
- Misses       9576     9875     +299     
- Partials     1003     1020      +17     

Flag	Coverage Δ
unittests	63.53% <17.24%> (-0.62%)	⬇️

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[RangiLyu]

LGTM

[ZwwWayne]

Recommend updating the README.md in this directory and pasting these commands in readme.
We can add a new section like Run YOLOv3 on IPU.
We do not need to add a new bash script here since the argument is simple.

[ZwwWayne]

Seems this PR depends on the progress on the IPU side, so it is pending.