gsys: Add ModelUnit virtual functions

lib/gsys/include/gsys/gsysModelUnitDrawArray.h

@@ -0,0 +1,18 @@
+#pragma once
+
+#include <hostio/seadHostIONode.h>
+
+namespace gsys {
+
+// TODO
+class ModelUnitDrawArray : public sead::hostio::Node {
+public:
+    struct CreateArg {
+        CreateArg();
+    };
+
+    ModelUnitDrawArray();
+    virtual ~ModelUnitDrawArray();
+};
+
+}  // namespace gsys