drivers: clock_control: nrf: add zero-latency-isr safe APIs

Add zero latency interrupt safe APIs to allow requesting and
releasing HFXO. These will be used from components running
in zero latency interrupt context, like the bluetooth stack.

Co-authored-by: Piotr Pryga <piotr.pryga@nordicsemi.no>

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