drivers: counter: Add user_data to alarm callback

Modify alarm callback to return user_data and channel_id.
Set_alarm and disable_alarm updated accordingly. Renamed
counter_*_ch_alarm to counter_*_channel_alarm. Updated test
and nrf implementations.

Updated doxygen comments.

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