rocketchip: rename identically names devices with _%d (#340)

* rocketchip: rename identically names devices with _%d

If you connect two devices with the same name in TL2 (totally ok there),
when they get put into the TL1 addrmap, one gets silently overwritten.
This renames the second occurance as _1, third as _2, and so on...

* junctions: blow if duplicates add to addrmap