tools: split io interface out

Splits the io interface out into its own file to decouple the
internal/sys from it.

Signed-off-by: Patrick Venture <venture@google.com>
Change-Id: I65860e32152ef49cd987c11eb408516e13fadb29
diff --git a/tools/test/io_mock.hpp b/tools/test/io_mock.hpp
index 4d18204..eddd6ff 100644
--- a/tools/test/io_mock.hpp
+++ b/tools/test/io_mock.hpp
@@ -1,6 +1,6 @@
 #pragma once
 
-#include "io.hpp"
+#include "io_interface.hpp"
 
 #include <gmock/gmock.h>