nrf52_bsim: Add tests of EGU

Adds automated tests for EGU peripheral.
These tests can be run on nrf52840dk_nrf52840
or on nrf52_bsim.

Signed-off-by: Robert Gałat <robert.galat@nordicsemi.no>
Co-authored-by: Filip Zajdel <filip.zajdel@nordicsemi.no>
Signed-off-by: Alberto Escolar Piedras <alberto.escolar.piedras@nordicsemi.no>