Add support for PrincipIoT F7 FC

[lukas-principiot]

Current Behavior

PrincipIoT F7 FC isn't supported

Desired Behavior

FC is supported

Suggested Solution

This FC is already supported in BF under target PRINCIPIOTF7 link
We can provide samples and resources as required, I'll be emailing shortly.

Who does this impact? Who is this for?

Users of the flight controller.

Additional context

Product page: https://principiot.com/flight-controller

[MrD-RC]

You need to let the manufacturer know that you would like an INAV target. Here is the new hardware policy.

https://github.com/iNavFlight/inav/blob/master/docs/policies/NEW_HARDWARE_POLICY.md

[lukas-principiot]

I am the manufacturer, I sent an email to the coredev account from my email lukas@principiot.com