[tof] Support VL53L8CX sync pin, for multiple boards

[lure23]

This is a welcome hardware addition. It allows one to externally trigger multiple sensors to start measurement at the same time.

• Needs practical testing

Initial coding for this was done in the ULD layer, but the author considers it may be a better approach to place it (only) behind a feature, e.g. enable_sync_pin.

Reasoning

Supporting the sync pin requires hardware routing of a signal - to be able to steer the additional pin from the host MCU. If you have the pin routed, why would you not use it?

Thus, instead of dynamically giving the yes/no for e.g. entering the scan mode, the sync pin could always be enabled (or not), and feature flags are a way to provide this.

Pros

• keeps the API simple (same whether you do single, multiple boards non-sync or multiple sync)

Cons

• is there a use case where the always-on/off approach would be too limiting. Think not.

Steps

Experiment with the syncing. It mainly becomes a thing of the vl_api level, since that's where we deal with multiple boards.

Then, fall on an approach that feels best.