drivers: clock_control: nrf2: split configs per driver

Currently the config CLOCK_CONTROL_NRF2 is used as a GLOB
style config which includes all "NRF2" drivers and related
configs.

With NRF2, clocks are treated as individidual devices
with individual device drivers. This commit split the
CLOCK_CONTROL_NRF2 config into device specific configs
and ifdefs. With this, drivers are selected individually
based on devicetree state as is common for most devices
drivers, and dependencies like NRFS and specific NRFS
services are selected by the specific driver which nees it.

Checks for CLOCK_CONTROL_NRF2 are updated to check for
existance of the clocks instead.

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