Definition of a function as weak symbol for reset in bootloader which prints an error message if no real implementation is compiled in and
the module `riotboot_reset` is not used. This is required if the module `usb_board_reset` is used to restart the board with an application via an USB CDC ACM interface, but the board's bootloader does not support a reset in the bootloader.
The board reset function `usb_board_reset_coding_cb` can be used on any CDC ACM interface. It is not necessary that the highlevel STDIO is used. Therefore, the call of the board reset function `usb_board_reset_coding_cb` has been moved from the USBUS STDIO CDC ACM implementation to USBUS CDC ACM implementation and is thus a feature of the USBUS CDC ACM interface that don't require any other functionality.
