device: add new device_deinit API

Add a new API to de-initialize a device. When a device is
de-initialized, it will release any resources it has acquired
(e.g. pins, memory, clocks, DMA channels, etc.) and its status
will be left as in its reset state.

It is the responsability of the caller to ensure that the device is
ready to be de-initialized.

For now, deinit call always initializes to NULL. New macros will be
introduced to not break existing device APIs.

Signed-off-by: Gerard Marull-Paretas <gerard.marull@nordicsemi.no>