IO initial states are correct

include/serial.h

@@ -0,0 +1,15 @@
+#pragma once
+
+#include <common.h>
+
+typedef struct {
+    u8 serial_data;
+    u8 serial_control;
+} serial_context;
+
+serial_context *serial_get_context();
+
+void serial_init();
+
+void serial_write(u16 address, u8 value);
+u8 serial_read(u16 address);