Add RTC driver

Signed-off-by: fpr <fabien.perroquin@wi6labs.com>

Author: fpr

cores/arduino/board.h

@@ -14,6 +14,7 @@ extern "C"{
 #include "digital_io.h"
 #include "hal_uart_emul.h"
 #include "hw_config.h"
+#include "rtc.h"
 #include "spi_com.h"
 #include "stm32_eeprom.h"
 #include "timer.h"