Redundant connections in 3D switchblocks

[soheilshahrouz]

In the RR graph created from an architecture with 3D switchblocks, each location has many CHANX node pairs that connect only to each other and are not connected to the rest of the RR graph. Because of this, the CHANZ cost factor has little effect on the bounding box (BB) cost.

For nodes that are connected to the rest of the graph, they sometimes connect wires on the same layer together, in addition to connecting wires between layers.