tests: drivers: i2c: target_api: add device_deinit test case

Add device_deinit test case which, in case there are two devices
using gpio loopbacks, deinits both controller and target devices,
then uses gpio to configure and toggle the pins of the bus, then
reinitializes both devices.

Signed-off-by: Bjarki Arge Andreasen <bjarki.andreasen@nordicsemi.no>