Hello world over serial

kernel/amd64/tss.c

@@ -0,0 +1,8 @@
+#include <libk/std.h>
+#include <amd64/tss.h>
+
+__attribute__((aligned(16))) static volatile struct tss tss;
+
+volatile struct tss *amd64_get_tss(void) {
+  return &tss;
+}