inputmethod: Don't disable them by default if there's a connected keyboard

If the user has chosen to have a virtual keyboard (i.e. prefered maliit
over none in the KCM) they should get it. If it's too annoying it should
either be disabled or we can fix it so it gets less in the way.

This is especially important since some hardware registers itself as a
keyboard even if it's not a fully functional keyboard.