Support for Ardusimple's simpleRTK2B+heading kit

Feature request to support direct connection of simpleRTK2B+heading kit to GPS 1

Although Ardupilot 4.1 supports GPS heading with two separate ublox F9P boards, Ardusimple is a popular kit, the simpleRTK2B+heading kit which has a small F9P Xbee board (the moving base) on top of another carrier F9P board (the rover) where the Rover outputs centimeter accurate PVT and Relposned data to pixhawk connector. Unfortunately Pixhawk's software currently expects this on separate connections. It doesn't seem that anyone has been able to make this work yet (perhaps csomy, but not clear)
See this [link ](https://discuss.ardupilot.org/t/rover-4-0-ardusimple-gps-yaw-debugging/55725)

**Describe the solution you'd like**
_A clear and concise description of what you want to happen._

**Describe alternatives you've considered**
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**Platform**
[ ] All
[ ] AntennaTracker
[ ] Copter
[ ] Plane
[ X ] Rover
[ ] Submarine

**Additional context**
This is for rover but perhaps also a good option for plane and copter, as this hardware package is considerable tighter and lighter.

Start by tracing how GPS 1 and the Pixhawk connector currently handle GPS heading from separate u-blox F9P connections. Review the simpleRTK2B+heading kit's PVT and Relposned output and the linked Rover GPS-yaw discussion. Done means the kit can provide centimeter-accurate position and heading through the expected connection, with Rover behavior validated.

Written by the indexing model from the issue text.