debug: coredump: stack top limit for current thread

Extend the functionality to limit the number of stack bytes
included in the core dump by allowing the limit to be
different for the current thread and remaining threads.

This is useful because it is more likely that we need more
call frames of the thread that was running when the
exception occurred than of the other threads in order to
analyze the exception.

Signed-off-by: Damian Krolik <damian.krolik@nordicsemi.no>