VPR: Add RR graph and other possibly necessary files

[acomodi]

VPR can accept pre-built data files, such as the Routing Resource Graph, the lookahead file or the placement delay matrix.

There are plans to make VPR output the location of these files natively so not to add extra requirements on the upstream tools, but at the moment this possibility is still yet to implement.

Therefore, we'd need to add the possibility to inject these files similarly to what happens for the arch.xml.

Files to be added that are not strictly necessary to run VPR are:

• RR graph: VPR command --read_rr_graph <path to rr graph>
• lookahead: VPR command --read_router_lookahead <path to rr lookahead>
• place delay matrix: VPR command --read_place_delay_matrix <path to place delay matrix>