feat(ACCESS): configure AUX serial port as "External module"

[raphaelcoeffic]

Description

This allows configuring the external access mod on runtime rather than by compilation option.

First, configure the hardware port (only available on AUX1 as AUX2 has no TX DMA)

Then the module can be chosen:

TODO:

• Companion support (separate PR)

[HThuren]

DA translation

#define TR_AUX_SERIAL_MODES            "FRA","Telem spejl","Telemetri ind","SBUS træner","LUA","CLI","GPS","Debug","SpaceMouse","Eksternt modul"

[Eldenroot]

CZ translation:

#define TR_AUX_SERIAL_MODES            "VYP","Telemetrie zrcadlení","Telemetrie vstup","SBUS Trenér","LUA","CLI","GPS","Debug","SpaceMouse","Externí modul"

[raphaelcoeffic]

@HThuren @Eldenroot please note that you guys can make PRs against this PR's branch ;-)

[HThuren]

Well, havn't tried (yet :-) ), have to figure out how to

[brainbubblersbest]

All Warp Levels Working on X12S Enterprise.
And in all Territorys ;D

[pfeerick]

Confirmed working on TX16S MK2 (ELRS) with externalaccess mod. R9M+2019 module running FCC firmware, and was able to register, bind, and configure options on both module and R9 SX receiver. If connecting directly to AUX1, inverters needed.

[edwardrf]

I'll apologise for my limited understanding of the firmware, I would like to understand this portion of the logic:

#if !defined(AUX_SERIAL_DMA_TX) || defined(EXTMODULE_USART)
  if (mode == UART_MODE_EXT_MODULE)
    return false;
#else // defined(AUX_SERIAL_DMA_TX) && !defined(EXTMODULE_USART)
  // UART_MODE_EXT_MODULE is only supported on AUX1, as AUX2 has no TX DMA
  if (mode == UART_MODE_EXT_MODULE && port_nr != SP_AUX1)
    return false;
#endif

Why AUX1 cannot be set to module if EXTMODULE_USART is defined? I am wondering if I can wire in another module internally in to my RadioMaster Pocket, which apparently has an empty UART port on the main board.

Thanks in advance.