drivers: counter: Add optional (D)PPI wrapping to nRF RTC driver

If top value is different than maximal top value (24 bits) then
wrapping must be handled. There are 2 ways to handle that:
- in software, by clearing the counter in the interrupt
- by HW, using (D)PPI which connects compare event with clear task

First option was already implemented but it has accumulative error.
Added PPI option which requires 1 PPI channels but has no accumulative
error.

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