px4_fmu-v2_default VTOL upgrade handling

[dagar]

Due to flash constraints we had to comment out the VTOL controller from px4_fmu-v2_default builds (#14342). We need to add logic at some level to notify any potential users.

[hamishwillee]

We should also add docs update to this effect.

• Will VTOL airframes still show up for FMUv2 boards? If not, we could add a note to https://docs.px4.io/master/en/config/airframe.html
• What exactly should users do if they want to use VTOL on an FMUv2 board?

We might:

• Update the first introduction to FC boards with this info https://docs.px4.io/master/en/getting_started/flight_controller_selection.html
• Explain the problem near "recommended boards": https://docs.px4.io/master/en/flight_controller/pixhawk_series.html#recommended

[hamishwillee]

@mrpollo The release notes indicated this would be going into 1.11 - is that the case? If so, it would be nice if you someone (@dagar ?) could answer the questions in #14381 (comment) -

Bit pointless for me to spend the time building and testing this when someone in the conversation could spend 45 seconds telling me.

[mrpollo]

@hamishwillee agreed, this needs to be resolved, I will chase down the answers and post-back here