Sub: Add support for TSYS01 on pixhawk 2

[patrickelectric]

Moved from: bluerobotics/ardusub#97
Original author: @jaxxzer

Feature request

The bus is hard coded, it needs to be determined at run time.

Platform
[ ] All
[ ] AntennaTracker
[ ] Copter
[ ] Plane
[ ] Rover
[x] Submarine

[jaxxzer]

The problem is the i2c bus to scan/probe is hardcoded to 1 here:

ardupilot/libraries/AP_TemperatureSensor/TSYS01.cpp

Line 18 in cd5c597

_dev = std::move(hal.i2c_mgr->get_device(1, TSYS01_ADDR));

We can update init() with a bus number parameter, and configure the bus according to the hardware, similar to how we select GND_EXT_BUS in system.cpp.

attention @Williangalvani

[jaxxzer]

https://github.com/ArduPilot/ardupilot/blob/master/ArduSub/system.cpp#L41