Allow count to be used for multiple arrays

I've the following definitions re-using the count for 2 arrays.

```
struct ActiveRoundsConfig {
round_index: 8,
ranging_role: 8,
_count_(responder_mac_list AND responder_slots): 8,
responder_mac_list: 8[],
responder_slot_scheduling: 8,
responder_slots: 8[],
}
```

Right now `_count_` only works for a single array.