xwayland/glamor: make wl_drm optional
With zwp_linux_dmabuf_feedback_v1, wl_drm becomes optional. There are also compositors (i.e., Chrome EXO) that support only zwp_linux_dmabuf_v1.
With zwp_linux_dmabuf_feedback_v1, wl_drm becomes optional. There are also compositors (i.e., Chrome EXO) that support only zwp_linux_dmabuf_v1.