SITL: Move the ENUM definition to the header file

[muramura]

ENUM definitions are not processes. There is a header file.
I think it would be better to move the definitions to the header file.

[amilcarlucas]

This removes the benefit of encapsulation.

What is the advantage of this change?

[muramura]

@amilcarlucas san.
I have defined the ENUM privately.
I think there are no benefits to defining the ENUM in the processing section.
You can obtain the definition through the editor.