ice40/import_routing: Major refactor of import_routing.
ice40/import_routing: Major refactor of import_routing.

Use the localname functionality in the rr_graph library.

Signed-off-by: Tim 'mithro' Ansell <b1c1d8736f20db3fb6c1c66bb1455ed43909f0d8@mith.ro>

SymbiFlow/symbiflow-arch-defs,SymbiFlow/symbiflow-arch-defs