Add support for PoE pins for Pi 4 / Rock Pi.

[vpetersson]

With the new design for the Raspberry Pi 3B+/4/Rock Pi 4, there are four new pins dedicated to the PoE HAT as can be seen here:

I was able to get things to work just fine using this board by manually wiring things up:

In order to add support for this, we need to add new pins to the board for this as you can't fit the board otherwise.

[shawaj]

Closing as we can stack directly on the RockPi as per below photo: