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>
Add some initial tests for the input subsystem, covering all the APIs in
both synchronous and thread mode.
Signed-off-by: Fabio Baltieri <fabiobaltieri@google.com>
