modules: hal_nordic: implement hfclk start/stop for nRF54H20.

Clock_control is currently not supported on nRF54H20.
This commit adds new way of handling the hfclk targeted for nRF54H20.

This solution shall be replaced once the clock_control is supported
for nRF54H20.

Signed-off-by: Piotr Koziar <piotr.koziar@nordicsemi.no>