Remove all init functions that do nothing, and provide a `NULL` to
*DEVICE*DEFINE* macros.
Signed-off-by: Gerard Marull-Paretas <gerard.marull@nordicsemi.no>
USB interface that may be used to send messages from a USB host to
the M4 processor in the S3B, and vice-versa.
Signed-off-by: Michal Sieron <msieron@antmicro.com>