[STM32L4] Add tests for asynchronous serial

Author: svastm

libraries/tests/utest/serial_asynch/serial_asynch.cpp

@@ -71,6 +71,9 @@
 #define TEST_SERIAL_ONE_TX_PIN PB_6  // UART1
 #define TEST_SERIAL_TWO_RX_PIN PG_9  // UART6
 
+#elif defined(TARGET_NUCLEO_L476RG)
+#define TEST_SERIAL_ONE_TX_PIN PB_10   // UART3
+#define TEST_SERIAL_TWO_RX_PIN PA_10   // UART1
 #elif defined(TARGET_RZ_A1H)
 #define TEST_SERIAL_ONE_TX_PIN P8_14  // UART4
 #define TEST_SERIAL_TWO_RX_PIN P8_11  // UART5