GPS: Add support for RTK GPS units
GPS: Add support for RTK GPS units

This includes the Trimble MB-TWO and similar devices. Tested including GPX streams.

Aerotenna/Firmware,Aerotenna/Firmware,krbeverx/Firmware,acfloria/Firmware,PX4/Firmware,Aerotenna/Firmware,mje-nz/PX4-Firmware,krbeverx/Firmware,krbeverx/Firmware,acfloria/Firmware,Aerotenna/Firmware,dagar/Firmware,dagar/Firmware,PX4/Firmware,PX4/Firmware,krbeverx/Firmware,krbeverx/Firmware,Aerotenna/Firmware,acfloria/Firmware,PX4/Firmware,mje-nz/PX4-Firmware,acfloria/Firmware,Aerotenna/Firmware,mje-nz/PX4-Firmware,krbeverx/Firmware,dagar/Firmware,mje-nz/PX4-Firmware,mje-nz/PX4-Firmware,dagar/Firmware,mje-nz/PX4-Firmware,krbeverx/Firmware,Aerotenna/Firmware,acfloria/Firmware,dagar/Firmware,dagar/Firmware,PX4/Firmware,acfloria/Firmware,PX4/Firmware,acfloria/Firmware,PX4/Firmware,mje-nz/PX4-Firmware,dagar/Firmware