console: untangle gfx & txt updates

Stop abusing displaysurface fields for text mode displays.
(bpp = 0, width = cols, height = lines).

Add flags to displaystate indicating whenever text mode display
(curses) or gfx mode displays (sdl, vnc, ...) are present.

Add separate displaychangelistener callbacks for text / gfx mode
resize & updates.

This allows to enable gfx and txt diplays at the same time and also
paves the way for more cleanups in the future.

Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
diff --git a/ui/spice-display.c b/ui/spice-display.c
index 5779fa8..fb99148 100644
--- a/ui/spice-display.c
+++ b/ui/spice-display.c
@@ -571,8 +571,8 @@
 }
 
 static DisplayChangeListener display_listener = {
-    .dpy_update  = display_update,
-    .dpy_resize  = display_resize,
+    .dpy_gfx_update  = display_update,
+    .dpy_gfx_resize  = display_resize,
     .dpy_refresh = display_refresh,
 };