[enhance]: Use RoIAlign implemented in MMCV for inference in CPU mode (#3930)
[enhance]: Use RoIAlign implemented in MMCV for inference in CPU mode (#3930)

* [enhance]: RoIAlign in mmcv is supported with aligned=False in CPU mode

* [Fix]: RoIPool doesn't have `aligned` attribute

* [enhance]: CPU inference with RoIPool is not supported currently (#3930)
open-mmlab/mmdetection,open-mmlab/mmdetection