debugger: handle gdb.TYPE_CODE_FUNC as "generic" type

This seems not to have been used in the past.

Change-Id: I6e6ce80b8cdd1f20477cde2718e5283a886bb87a
Reviewed-by: Eike Ziller <eike.ziller@digia.com>
Reviewed-by: hjk <qthjk@ovi.com>