tests: drivers: clock_control_api: move startup time to Kconfig

Moved target dependent startup time from header file to
Kconfig option to allow adding new targets with new .conf
file rather that modyfing source of the test. Adjusted
startup time for nRF54L09 and nRF54L20.

Signed-off-by: Michał Stasiak <michal.stasiak@nordicsemi.no>