add board_reset_to_bootloader(), try to implement that for ch32v203 but not working yet

hw/bsp/board_api.h

@@ -72,6 +72,9 @@ void board_init(void);
 // Init board after tinyusb is initialized
 void board_init_after_tusb(void) TU_ATTR_WEAK;
 
+// Jump to bootloader
+void board_reset_to_bootloader(void) TU_ATTR_WEAK;
+
 // Turn LED on or off
 void board_led_write(bool state);