soc: nordic: Fix the way of enabling clock control for nRF54H Series

This is a follow-up to commit 7a2ce288.

Do not enable clock control by default on nRF54H Series SoCs when
the system timer is present, because clock control is not needed
for this purpose there.

Add missing `default y` in the CLOCK_CONTROL_NRF2 Kconfig option that
enables compilation of clock control drivers for nRF54H Series.
This way modules that actually require clock control (like drivers
that use radio) will be able to enable it using the generic option
(CLOCK_CONTROL), not the above one that is specific for nRF54H.

Update accordingly applications that referenced the CLOCK_CONTROL_NRF2
option.

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