samples: boards: nrf: Add an nrfx peripheral resource sharing sample

Add a sample that shows how to use in Zephyr nRF peripherals that
share the same ID and base address. Such peripherals cannot be used
simultaneously, but it is possible to switch between them. However,
currently it is not possible with Zephyr APIs, only using nrfx drivers
directly. This sample shows how to realize such switching for selected
peripheral instances while using standard Zephyr drivers for others.

Signed-off-by: Andrzej Głąbek <andrzej.glabek@nordicsemi.no>