utils: add enabling Wayland feature into gdm-disable-wayland
We can disable Wayland in runtime by invoking gdm-disable-wayland. However, we may also want to enable Wayland in runtime for some reasons.
This commit extends gdm-disable-wayland by parsing the argument. It not only keeps disable Wayland by default, but also parses the argument if users want to enable the Wayland by passing "false", "FALSE" or "0" to gdm-disable-wayland command.