Refactor bootloader_jump() implementations (#15450)

* Refactor `bootloader_jump()` implementations

* Fix tests?

* Rename `atmel-samba` to `md-boot`

platforms/chibios/bootloaders/gd32v_dfu.c

@@ -0,0 +1,40 @@
+/* Copyright 2021 QMK
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program 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 General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include "bootloader.h"
+
+#include <ch.h>
+
+#define DBGMCU_KEY_UNLOCK 0x4B5A6978
+#define DBGMCU_CMD_RESET 0x1
+
+__IO uint32_t *DBGMCU_KEY = (uint32_t *)DBGMCU_BASE + 0x0CU;
+__IO uint32_t *DBGMCU_CMD = (uint32_t *)DBGMCU_BASE + 0x08U;
+
+__attribute__((weak))
+void bootloader_jump(void) {
+    /* The MTIMER unit of the GD32VF103 doesn't have the MSFRST
+     * register to generate a software reset request.
+     * BUT instead two undocumented registers in the debug peripheral
+     * that allow issueing a software reset. WHO would need the MSFRST
+     * register anyway? Source:
+     * https://github.com/esmil/gd32vf103inator/blob/master/include/gd32vf103/dbg.h */
+    *DBGMCU_KEY = DBGMCU_KEY_UNLOCK;
+    *DBGMCU_CMD = DBGMCU_CMD_RESET;
+}
+
+/* Jumping to bootloader is not possible from user code. */
+void enter_bootloader_mode_if_requested(void) { }