plugins: fix compilation when EGL/GLX is disabled
plugins: fix compilation when EGL/GLX is disabled

The compiler might complain of gst_vaapi_create_display_from_handle() being
unused if both EGL and GLX are disabled. This patch avoid that compilation
error.

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