stm32: flash: pull lock/unlock up to common_f.

This is a common operation, so definition in _all, and every part except
l0/l1 have the same implementation.  Bring in an _f file too.

lib/stm32/common/flash_common_f.c

@@ -0,0 +1,41 @@
+/** @addtogroup flash_file
+ *
+ */
+
+/*
+ * 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/>.
+ */
+
+/**@{*/
+
+#include <libopencm3/stm32/flash.h>
+
+
+void flash_unlock(void)
+{
+	/* Clear the unlock state. */
+	FLASH_CR |= FLASH_CR_LOCK;
+
+	/* Authorize the FPEC access. */
+	FLASH_KEYR = FLASH_KEYR_KEY1;
+	FLASH_KEYR = FLASH_KEYR_KEY2;
+}
+
+void flash_lock(void)
+{
+	FLASH_CR |= FLASH_CR_LOCK;
+}
+