stm32/extint.h: Use correct EXTI lines for RTC interrupts.
#define EXTI_USB_OTG_FS_WAKEUP (18)
#define EXTI_ETH_WAKEUP (19)
#define EXTI_USB_OTG_HS_WAKEUP (20)
-#if defined(STM32F0)
+#if defined(STM32F0) || defined(STM32L4)
#define EXTI_RTC_TIMESTAMP (19)
#define EXTI_RTC_WAKEUP (20)
#else
