drivers: counter: nrfx_rtc: Add option to use ZLI interrupt

Extended driver configuration in device tree to enable ZLI interrupt.
When zli is set in the device tree then event handlers for alarm and
top is called in ZLI interrupt context. It means that kernel primitives
cannot be used there.

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