doc: efm32: rtc: tag and include in generated output

Includes the sutb file ncessary to find shared headers without any apis

lib/efm32/common/rtc_common.c

@@ -0,0 +1,16 @@
+/** @addtogroup rtc_file RTC peripheral API
+ * @ingroup peripheral_apis
+ * @brief Real Time Clock helper functions.
+ *
+ * <b>NO</b> helper functions exist. Only header definitions are available.
+ * Delete these lines if/when you add actual helper APIs.
+ * @sa rtc_defines
+ * @copyright See @ref lgpl_license
+ */
+
+#include <libopencm3/efm32/rtc.h>
+
+/**@{*/
+
+/**@}*/
+

lib/efm32/ezr32wg/Makefile

@@ -50,6 +50,7 @@ OBJS += letimer_common.o
 OBJS += msc_common.o
 OBJS += prs_common.o
 OBJS += rmu_common.o
+OBJS += rtc_common.o
 OBJS += timer_common.o
 OBJS += wdog_common.o
 

lib/efm32/lg/Makefile

@@ -50,6 +50,7 @@ OBJS += letimer_common.o
 OBJS += msc_common.o
 OBJS += prs_common.o
 OBJS += rmu_common.o
+OBJS += rtc_common.o
 OBJS += timer_common.o
 OBJS += wdog_common.o
 

lib/efm32/wg/Makefile

@@ -50,6 +50,7 @@ OBJS += letimer_common.o
 OBJS += msc_common.o
 OBJS += prs_common.o
 OBJS += rmu_common.o
+OBJS += rtc_common.o
 OBJS += timer_common.o
 OBJS += wdog_common.o