ITM: `configure` lacks API for stimulus registers

I propose something akin to:
```rust
itm.configure(ITMConfiguration {
    // ...
    stim: Stimulus::EnableAll
}
```
```rust
itm.configure(ITMConfiguration {
    // ...
    stim: Stimulus::EnableSome([0..5, 8..31]),
}
```

Better review `iprint` and `iprintln` and see if they make any assumptions about the registers.