Scatter-gather patterns for 3D architectures

[soheilshahrouz]

This PR includes the following changes:

1. Creates nodes and edges in RR graph based on scatter-gather patterns specifed in the architecture file.
2. Updates router lookahead map to handle CHANZ nodes properly.
3. Computes indexed data for CHANZ nodes.
4. Removes 3-d (with above and under) switch blocks from code

[soheilshahrouz]

Titan 2D

Metric	master.txt	feature.txt
vtr_flow_elapsed_time	1	1.01962283887379
max_vpr_mem	1	0.988996538527656
pack_time	1	1.0159114629532
placed_wirelength_est	1	1
place_time	1	1.03434272913768
placed_CPD_est	1	1
routed_wirelength	1	1
critical_path_delay	1	1
crit_path_route_time	1	1.01068496559616

[soheilshahrouz]

Comparison between 3D and 2D architectures on this branch

6 upward and 6 downward connections everywhere
The delay of an interdie mux twice an L4 (118ps vs. 59ps)
fanin = fanout = 30

Titan other

Pack Time	Place Time	Route Time	WL	CPD
0.988	0.997	1.009	0.925	0.968

Titan 23

Pack Time	Place Time	Route Time	WL	CPD
1.013	0.985	0.963	0.898	0.899

Comparison between 3D and 2D architectures on master
Titan other

fanin = fanout = 60
No control over the number of CHANZ connections

Metric	pack time	place time	route time	WL	CPD
3D/2D ratio	0.983	0.997	1.109	0.945	0.970

[vaughnbetz]

Looks good! I'm reviewing now; if you can resolve the conflicts that would be good.

[vaughnbetz]

Looks good so far. Done up to (but not including) libs/librrgraph/src/io/gen/rr_graph_uxsdcxx.h

No critical changes flagged here, but some clean ups / commenting.