debug messages: implement dynamic debug

Heavily inspired off linux kernel's dynamic debug:
 * add a /sys/kernel/debug/dynamic_debug/control file
 (accessible from linux side in /sys/class/mcos/mcos0/sys/kernel/debug/dynamic_debug/control)
 * read from file to list debug statements (currently limited to 4k in size)
 * write to file with '[file foo ][func bar ][line [x][-[y]]] [+-]p' to change values

Side effects:
 * reindented all linker scripts, there is a new __verbose section
 * added string function strpbrk

Change-Id: I36d7707274dcc3ecaf200075a31a2f0f76021059

arch/x86_64/kernel/cpu.c

@@ -31,6 +31,7 @@
 #include <prctl.h>
 #include <page.h>
 #include <kmalloc.h>
+#include <debug.h>
 
 #define LAPIC_ID            0x020
 #define LAPIC_TIMER         0x320
@@ -69,11 +70,8 @@
 //#define DEBUG_PRINT_CPU
 
 #ifdef DEBUG_PRINT_CPU
-#define dkprintf kprintf
-#define ekprintf kprintf
-#else
-#define dkprintf(...) do { if (0) kprintf(__VA_ARGS__); } while (0)
-#define ekprintf kprintf
+#undef DDEBUG_DEFAULT
+#define DDEBUG_DEFAULT DDEBUG_PRINT
 #endif
 
 static void *lapic_vp;