meson: Allow building on a Wayland-only environment
Currently, it is not possible to build spice-gtk on a Wayland-only environment due to the x11 dependency in meson.
Since commit a7381b08 ("Allow to build without X11 gdk backend) it is possible to build spice-gtk without X11 GDK backend, so remove x11 dependency in meson as well.
Signed-off-by: Fabio Estevam festevam@denx.de