New debug scheme with explicit debug channels declaration.

diff --git a/misc/system.c b/misc/system.c
index f7e7708..14f73b9 100644
--- a/misc/system.c
+++ b/misc/system.c
@@ -9,6 +9,8 @@
 #include "services.h"
 #include "debug.h"
 
+DEFAULT_DEBUG_CHANNEL(system)
+
 typedef struct
 {
     SYSTEMTIMERPROC callback;  /* NULL if not in use */