Added support for LibreTiny IoT chips

https://github.com/libretiny-eu/libretiny

Tested with v1.8.0 on a BK7231N and the following build flags:
  -DMASK_VERSION=0x57B0
  -DKNX_NO_SPI
  -DKNX_FLASH_OFFSET=0x1DB000

examples/knx-demo/knx-demo.ino

@@ -58,7 +58,11 @@ void setup()
     Serial.begin(115200);
     ArduinoPlatform::SerialDebug = &Serial;
 
+#ifdef LIBRETINY
+    srandom(millis());
+#else
     randomSeed(millis());
+#endif
 
 #if MASK_VERSION != 0x07B0 && (defined ARDUINO_ARCH_ESP8266 || defined ARDUINO_ARCH_ESP32)
     WiFiManager wifiManager;

examples/knx-demo/platformio-ci.ini

@@ -96,3 +96,17 @@ build_flags =
   -DKNX_FLASH_SIZE=4096
   -D PIO_FRAMEWORK_ARDUINO_ENABLE_RTTI
   -Wno-unknown-pragmas
+
+;--- LibreTiny BK7231N ------------------------------------
+[env:BK7231N_ip]
+platform = libretiny
+board = cbu
+framework = arduino
+lib_deps =
+  knx
+
+build_flags =
+  -DMASK_VERSION=0x57B0
+  -DKNX_NO_SPI
+  -DKNX_FLASH_OFFSET=0x1DB000
+  -Wno-unknown-pragmas

examples/knx-demo/platformio.ini

@@ -168,4 +168,22 @@ build_flags =
   -DMASK_VERSION=0x07B0
   -DKNX_FLASH_SIZE=4096
   -D PIO_FRAMEWORK_ARDUINO_ENABLE_RTTI
+  -Wno-unknown-pragmas
+
+;--- LibreTiny BK7231N ------------------------------------
+[env:BK7231N_ip]
+platform = libretiny
+board = cbu
+framework = arduino
+; We consider that the this projects is opened within its project directory
+; while working with VS Code.
+lib_extra_dirs = ../../../
+
+lib_deps =
+  knx
+
+build_flags =
+  -DMASK_VERSION=0x57B0
+  -DKNX_NO_SPI
+  -DKNX_FLASH_OFFSET=0x1DB000
   -Wno-unknown-pragmas