Fix trainer sbus taranis

[bug400]

Fixes #5139

Summary of changes:
The definition for trainer module sbus/cppm are in the "Trainer / Trainee from the module bay" section of hal.h for Taranis radios. The initialization of the module ports is in trainer_init_module_sbus() (trainer.cpp) and isTrainerMode available (gui_common.cpp). In both files the proper init of the UART is controlled by the identifier TRAINER_MODULE_SBUS_USART which is not defined in the hal section for Taranis radios. Therefore I reintroduced an identifier TARANIS_MODULE_SBUS.
Trainer/SBUS function tested on 2.10.1 and 2.11 with radio Taranis QX7ACCESS. Tested on 2.11 with Tx16s simulator only.

[raphaelcoeffic]

@bug400 adding TRAINER_MODULE_SBUS makes no sense to me, especially because this is going to break it for everyone else (I don't see this #define anywhere else).

In fact, it should be sufficient to just remove the #if defined(...) and test both potential ports with the heartbeat pin being the preferred one and falling back automatically to S.PORT.

[raphaelcoeffic]

@bug400 could please check #5149?

[pfeerick]

Closing as #5149 resolves this in a cleaner manner