(New?) build flags required to get this running in platformio

Hi Owen,

Firstly, thanks for putting this up - it's rough with the new CANFD peripheral still!

I at first had a little trouble getting up and running, but adding enabling the `HAL_FDCAN_MODULE_ENABLED` build flag fixed that!

```ini
build_flags = 
    -DHAL_FDCAN_MODULE_ENABLED
```

Leaving this here for the next person as much as you