build: fix meson build error when without x11.
build: fix meson build error when without x11.

meson -Dwith_x11=no build_dir
can not success build the project because the glx is still enabled.
We need to disable GLX when X11 is disabled.

ceyusa/gstreamer-vaapi,ceyusa/gstreamer-vaapi,GStreamer/gstreamer-vaapi,GStreamer/gstreamer-vaapi