tmf: Define the StateChangeInput's event type at the constructor

tmf: Define the StateChangeInput's event type at the constructor

instead of using an abstract method just for that.

With this we can also check in the abstract class itself if the
event type is the right one before calling the method from the
sub-class.

Change-Id: I0cbce6c87e3ec51acfac4061c9db38f32bbcce9a
Signed-off-by: Alexandre Montplaisir <alexmonthy@voxpopuli.im>
Reviewed-on: https://git.eclipse.org/r/7807
Tested-by: Hudson CI