stm32:l4: Add RTC

Use common, some additional registers missing

include/libopencm3/stm32/l4/rtc.h

@@ -0,0 +1,36 @@
+/** @defgroup rtc_defines RTC Defines
+
+@brief <b>Defined Constants and Types for the STM32L4xx RTC</b>
+
+@ingroup STM32L4xx_defines
+
+@version 1.0.0
+
+@date 18 December 2017
+
+LGPL License Terms @ref lgpl_license
+ */
+
+/*
+ * This file is part of the libopencm3 project.
+ *
+ * This library is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Lesser General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public License
+ * along with this library.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#ifndef LIBOPENCM3_RTC_H
+#define LIBOPENCM3_RTC_H
+
+#include <libopencm3/stm32/common/rtc_common_l1f024.h>
+
+#endif

include/libopencm3/stm32/rtc.h

@@ -30,6 +30,8 @@
 #       include <libopencm3/stm32/f4/rtc.h>
 #elif defined(STM32L1)
 #       include <libopencm3/stm32/l1/rtc.h>
+#elif defined(STM32L4)
+#       include <libopencm3/stm32/l4/rtc.h>
 #else
 #       error "stm32 family not defined."
 #endif

lib/stm32/l4/Makefile

@@ -51,6 +51,7 @@ OBJS            += i2c_common_v2.o
 OBJS            += usart_common_all.o usart_common_v2.o
 OBJS            += dma_common_l1f013.o
 OBJS            += iwdg_common_all.o
+OBJS            += rtc_common_l1f024.o
 
 VPATH += ../../usb:../:../../cm3:../common
 VPATH += ../../ethernet