sdbus++: generate callback methods for server bindings

Create sd-bus message handler methods as callbacks for object
method calls.  These generated callbacks will extract the
parameters from the message, call the virtual-method implementation,
and pack the response into a method-return message, which is sent
back to the caller.

Change-Id: Ia3872bbbbfdb57375a1ffdde7e64296271cdd532
Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
diff --git a/tools/sdbus++ b/tools/sdbus++
index 6606d07..6051046 100755
--- a/tools/sdbus++
+++ b/tools/sdbus++
@@ -6,7 +6,8 @@
 def main():
     valid_types = { 'interface': sdbusplus.Interface }
     valid_processes = { 'markdown' : "markdown",
-                        'server-header' : "server_header" }
+                        'server-header' : "server_header",
+                        'server-cpp' : "server_cpp" }
 
     parser = argparse.ArgumentParser(description='Process sdbus++ YAML files.')