feat(T16,T18): Add support for USART6/AUX2, incl. internal GPS, if Bluetooth is not enabled

[rotorman]

This PR adds two features to Jumper T16 & T18:

1. enables USART6/AUX2, if Bluetooth is not used/activated during build
2. enables GPS support

USART3/AUX1 pins can be reached via debug header. Here T16:

T18:

and

USART6/AUX2 can be reached via FrSky Bluetooth module header on the mainboard (here pinout for RX and TX):

@Stinky80 tested using these changes the GPS functionality and USART6/AUX2 successfully on his Jumper T16 and he promised to add here some proof pictures tomorrow.

[Stinky80]

as you can see it works for t16 :)

[Stinky80]

on the weekend I will be able to take a photo of how it was done inside, and also some modding will get there for a subsequent upgrade :)

[rotorman]

@elecpower a quick test with Companion shows that for Jumper T16 and T18, AUX1 and AUX2 are already listed and GPS is selectable, thus am I assuming correctly that no further changes due to this PR will be required to Companion?

P.S. The reason you are not seeing AUX1 listed on @Stinky80 first screenshot above is, that he is using here another WiP hack from me that adds touch screen support to T16 via I2C2 that is on the same pins as AUX1/USART3 (when this is well tested, there will be a separate PR about this, but for now sneak peek can be seen in rotorman@8a67a51 ).

[elecpower]

@elecpower a quick test with Companion shows that for Jumper T16 and T18, AUX1 and AUX2 are already listed and GPS is selectable, thus am I assuming correctly that no further changes due to this PR will be required to Companion?

Would appear Companion has you covered

[rotorman]

@pfeerick Do I have your blessing for merging this PR?

[Stinky80]

the power line is weak for long wires connecting for standard gps module .. you need to use either a 5v line on the radio. or low voltage gps module 3.3v

This module GPS installing in to horus x12s