ASM-to-PIL linker: Use bus

[georgwiese]

Depends on #1497

Currently, our linker translates links to native lookup or permutation arguments. In the future, it should instead:

1. Generate a lookup / permutation annotation (see Witgen annotations in PIL #1378).
2. Call the (not yet implemented) bus_send and bus_recieve functions (Implement basic bus #1497). For now, we'd create one accumulator for each lookup / permutation & machine. In future implementations (see VADCOP design #424), we can be smarter and have one accumulator per machine.

Step (1) could actually be skipped (keeping the native lookups / permutations), because in the upcoming CompositeBackend (#1470) they are removed anyway (but still there to help with witness generation).