We are currently working on replacing the overloaded `TopPbType` with a separate `Tile` tile which contains `PbType` objects. See the [VPR Proposal for supporting equivalent placement types](https://docs.google.com/document/d/1LQ0H2C9IFnCVtSuaniCs1dDmBoMBWwBQLKAGuo_kSc0/edit) Doc.