inventory_mac: Migrate code out of other places

Change-Id: I5a84c07eebad1b9b0dc535a47edbf6bf0f72b6cb
Signed-off-by: William A. Kennington III <wak@google.com>
diff --git a/src/inventory_mac.hpp b/src/inventory_mac.hpp
new file mode 100644
index 0000000..f7aec32
--- /dev/null
+++ b/src/inventory_mac.hpp
@@ -0,0 +1,24 @@
+#pragma once
+#include <memory>
+
+namespace sdbusplus::bus
+{
+class bus;
+}
+
+namespace phosphor::network
+{
+
+class Manager;
+
+namespace inventory
+{
+
+struct Runtime
+{
+    virtual ~Runtime() = default;
+};
+std::unique_ptr<Runtime> watch(sdbusplus::bus::bus& bus, Manager& m);
+
+} // namespace inventory
+} // namespace phosphor::network