stm32/extint: Use correct EXTI channels on H7 MCUs for RTC events.
#if defined(STM32F0) || defined(STM32L4)
#define EXTI_RTC_TIMESTAMP (19)
#define EXTI_RTC_WAKEUP (20)
+#elif defined(STM32H7)
+#define EXTI_RTC_TIMESTAMP (18)
+#define EXTI_RTC_WAKEUP (19)
#else
#define EXTI_RTC_TIMESTAMP (21)
#define EXTI_RTC_WAKEUP (22)
