soc: nordic: add fn for setting constlat mode

Nordic SoCs implement an event system, for which the system can
optimize for low latency/high power or low power.

Add soc level implementation of reference counted API which will
optimize for low latency if any part of the system requires it.

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