Make sure that profiling can only be started if debugging is enabled.

Enabling the profiler doesn't make much sense if there is no debug
service as the messages can't be sent anywhere then. Furthermore, the
profiler instance is only properly initialized if debugging is enabled
and thus enabling profiling without debugging being enabled can cause
problems.

Change-Id: I784a110126d45a9a2bc9d9e14d9a22e2980c3a42
Reviewed-by: Kai Koehne <kai.koehne@digia.com>