hal_nordic: Change scheme for RTC and TIMER reservation

In general, RTC and TIMER driver implements counter API but there
are exception when those peripherals are used in a custom way
(e.g. for system timer or bluetooth). In that case, system must
prevent using counter based on a reserved instance. Previously,
it was managed by Kconfig options but that cannot be maintained
when switching to devicetree configuration of the counter driver.

A new approach removes Kconfig options and instead adds static
asserts in the files which are using direct peripherals. Those
asserts check if given node is not enabled in the device tree.

Signed-off-by: Krzysztof Chruscinski <krzysztof.chruscinski@nordicsemi.no>