feat: Support for ext. Multiplex MLink JR type module (#3352)

* introducing external MLink module telemetry as module PPM subtype

* implemented fix for sensor discovery display not showing all detected sensors (is in separate PR too)

implemented PPM subtypes in Companion

* add PPM subtype to model printer

finalize subtypes for PPM in Companion

* added logic to try to use HW UART with inverters turned off first (e.g. NV14), then, if not successfull use soft serial inverted (== uninverted data due to HW inverters on PCB)

changed start bit detection IRQ priority from 5 to the previous 0 (also in separate PR)

* extended telemetry timeout to 2s due to slow Mlink RSSI update rate

* changed the "NOTLM" sub-type texts to:

- "No Telem" for 128x64 (this is the max numbers of characters it can take)
- "No Telemetry" everything else including Companion

* Companion:

- lower case 1st charachter on PpmSubTypeStrings to ppmSubTypeStrings
- added telemetry hooks for ppmSubTypeStrings stringx

* simplified serial port initialization for MLink telemetry

* editorial change: corrected obsolete comment

radio/src/pulses/ppm.cpp

@@ -27,6 +27,8 @@
 
 #include "opentx.h"
 
+#include "telemetry/mlink.h"
+
 // Minimum space after the last PPM pulse in us
 #define PPM_SAFE_MARGIN 3000 // 3ms
 
@@ -158,3 +160,37 @@ const etx_proto_driver_t PpmDriver = {
   .sendPulses = ppmSendPulses,
   .processData = nullptr,
 };
+
+//
+// additions for PPM with external MLink Module telemetry
+//
+
+static void* ppmMLinkInit(uint8_t module);
+
+const etx_proto_driver_t PpmDriverMLink = {
+  .protocol = PROTOCOL_CHANNELS_PPM_MLINK,
+  .init = ppmMLinkInit,
+  .deinit = ppmDeInit,
+  .sendPulses = ppmSendPulses,
+  .processData = processExternalMLinkSerialData,
+};
+
+static etx_serial_init ppmMLinkSerialParams = {
+  .baudrate = PPM_MSB_BAUDRATE,
+  .encoding = ETX_Encoding_8N1,
+  .direction = ETX_Dir_RX,
+  .polarity = ETX_Pol_Inverted,
+};
+
+static void* ppmMLinkInit(uint8_t module) {
+  etx_module_state_t *mod_st = (etx_module_state_t *)ppmInit(module);
+  
+  if (!mod_st) 
+    return nullptr;
+
+  if (!modulePortInitSerial(module, ETX_MOD_PORT_UART, &ppmMLinkSerialParams)) {
+      modulePortInitSerial(module, ETX_MOD_PORT_SPORT_INV, &ppmMLinkSerialParams);
+  }
+
+  return (void*)mod_st;
+}