stm32l4: enable common exti functionality

tested on l476 disco board.

include/libopencm3/stm32/exti.h

@@ -36,6 +36,8 @@
 #       include <libopencm3/stm32/l0/exti.h>
 #elif defined(STM32L1)
 #       include <libopencm3/stm32/l1/exti.h>
+#elif defined(STM32L4)
+#       include <libopencm3/stm32/l4/exti.h>
 #else
 #       error "stm32 family not defined."
 #endif

include/libopencm3/stm32/l4/exti.h

@@ -0,0 +1,23 @@
+/*
+ * 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_EXTI_H
+#define LIBOPENCM3_EXTI_H
+
+#include <libopencm3/stm32/common/exti_common_all.h>
+
+#endif

lib/stm32/l4/Makefile

@@ -43,6 +43,7 @@ OBJS		= adc.o flash.o pwr.o rcc.o
 # common/shared objs
 OBJS            += rcc_common_all.o
 OBJS            += gpio_common_all.o gpio_common_f0234.o
+OBJS            += exti_common_all.o
 OBJS            += adc_common_v2.o adc_common_v2_multi.o
 OBJS            += crc_common_all.o crc_v2.o
 OBJS            += crs_common_all.o