Stm32 rtc small patches
* RTC: canceling an alarm marks it as inactive
* STM32L4, STM32F4, STM32F7 RTC: fix reading alarm value that is more than 24h in future
* STM32F0 RTC: fix backup register count in stm32_rtcc.h
All other STM32: SHIFTR_SUBFS_MASK was correct in STM32F0 only
* STM32L1: use correct EXTI line definitions
Approved-by: Gregory Nutt <gnutt@nuttx.org>