nox: add default uart for smart audio
USART2_PA3PA2
#define ENABLE_SMART_AUDIO
+#define SMART_AUDIO_USART USART_PORT1
#if defined(RX_SBUS) || defined(RX_DSMX_2048) || defined(RX_DSM2_1024) || defined(RX_CRSF) || defined(RX_IBUS) || defined(RX_FPORT) || defined(RX_UNIFIED_SERIAL)
#define RX_USART USART_PORT2
