drivers: clock_control: nrf: Use IRQ number symbol generated from DT

Use the symbol generated from DT so that it is common for nRF9160
and nRF5 family SoCs. To avoid artificial renaming of CLOCK_POWER_IRQn
to POWER_CLOCK_IRQn.

For nRF5 family SoCs clock nodes were not defined so far, thus they are
added so that the proper DT symbol is generated for them as well.

Signed-off-by: Andrzej Głąbek <andrzej.glabek@nordicsemi.no>