[RTC] Allow to enable HAL module only

Define `HAL_RTC_MODULE_ONLY` in `build_opt.h` or `hal_conf_extra.h`
allow HAL RTC module usage without any usage by the core.

Fixes stm32duino#697

Signed-off-by: Frederic Pillon <frederic.pillon@st.com>

Author: fpistm

cores/arduino/stm32/rtc.c

@@ -38,7 +38,7 @@
 
 #include "rtc.h"
 
-#ifdef HAL_RTC_MODULE_ENABLED
+#if defined(HAL_RTC_MODULE_ENABLED) && !defined(HAL_RTC_MODULE_ONLY)
 #if defined(STM32MP1xx)
 /**
  * Currently there is no RTC driver for STM32MP1xx. If RTC is used in the future
@@ -704,6 +704,6 @@ void RTC_Alarm_IRQHandler(void)
 }
 #endif
 
-#endif /* HAL_RTC_MODULE_ENABLED */
+#endif /* HAL_RTC_MODULE_ENABLED  && !HAL_RTC_MODULE_ONLY */
 
 /************************ (C) COPYRIGHT STMicroelectronics *****END OF FILE****/

cores/arduino/stm32/rtc.h

@@ -45,7 +45,7 @@
 #include "backup.h"
 #include "clock.h"
 
-#ifdef HAL_RTC_MODULE_ENABLED
+#if defined(HAL_RTC_MODULE_ENABLED) && !defined(HAL_RTC_MODULE_ONLY)
 
 #ifdef __cplusplus
 extern "C" {
@@ -170,7 +170,7 @@ void detachAlarmCallback(void);
 }
 #endif
 
-#endif /* HAL_RTC_MODULE_ENABLED */
+#endif /* HAL_RTC_MODULE_ENABLED  && !HAL_RTC_MODULE_ONLY */
 
 #endif /* __RTC_H */