dts: nrf: Move the HCI rng node to the SoC common file

Since the HCI entropy device is a software construct that is able to
provide entropy bytes by retrieving them from a Bluetooth Controller,
generalize it by moving it to the Nordic common DTS code. Additionally
move the chosen nodes from the nRF5340 DK board files to the SoC ones.

Signed-off-by: Carles Cufi <carles.cufi@nordicsemi.no>