[Enhance] Update PointFusion (#791)

* update point fusion

* remove LIDAR hardcode

* move get_proj_mat_by_coord_type to utils

* fix lint

* remove todo

* fix lint

mmdet3d/models/fusion_layers/point_fusion.py

@@ -32,7 +32,7 @@ def point_sample(img_meta,
         points (torch.Tensor): Nx3 point cloud in LiDAR coordinates.
         proj_mat (torch.Tensor): 4x4 transformation matrix.
         coord_type (str): 'DEPTH' or 'CAMERA' or 'LIDAR'.
-        img_scale_factor (torch.Tensor): Scale factor with shape of \
+        img_scale_factor (torch.Tensor): Scale factor with shape of
             (w_scale, h_scale).
         img_crop_offset (torch.Tensor): Crop offset used to crop
             image during data augmentation with shape of (w_offset, h_offset).