Add a debug output utility.

zion/debug/debug.cpp

@@ -0,0 +1,13 @@
+#include "debug/debug.h"
+
+#include "common/port.h"
+
+#define COM1 0x3f8
+
+void dbgln(const char* str) {
+  while (*str != 0) {
+    outb(COM1, *str);
+    str++;
+  }
+  outb(COM1, '\n');
+}

zion/debug/debug.h

@@ -0,0 +1,3 @@
+#pragma once
+
+void dbgln(const char *str);