Add convinence wrappers to query DisplaySurface properties.
Simliar to ds_get_*, but operating in the DisplaySurface
not the DisplayState.
With this patch in place ui frontents can stop using DisplayState
in the rendering code paths, they can simply operate using the
DisplaySurface passed in via dpy_gfx_switch callback.
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
626e3b34e3