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.
The private parts need USB definitions (and are thus preferably used
from USB_H_USER_IS_RIOT_INTERNAL compilation units). Functions like
usb_board_reset_in_bootloader do not depend on USB headers for their
definitions and are fair game throughout the application even for
generic RIOT USB devices.
