Allow selectively disabling debug features to reduce code/data size

Allow selectively disabling debug features to reduce code/data size

Kdebug already contained preprocessor symbols for turning off ASSERT2()
messages and trace, but it was not possible to override them from
cfg_debug.h.

This patch renames the old options to use positive logic and add a
third option to enable walls. The defaults remain unchanged.

TODO: add these settings to cfg/cfg_debug.h, along with some
documentation.

git-svn-id: https://src.develer.com/svnoss/bertos/trunk@4774 38d2e660-2303-0410-9eaa-f027e97ec537