Debug printing functions

src/kernel/include/debug.h

@@ -0,0 +1,9 @@
+#pragma once
+#include <stddef.h>
+#include <stdarg.h>
+
+void debug_putch(char c);
+void debug_putsn(char *s, size_t n);
+void debug_puts(char *s);
+void debug_vprintf(char *fmt, va_list args);
+void debug_printf(char *fmt, ...);