ui/vnc: Support shared surface for most pixman formats

At least all the ones I've tested. We make the assumption that
pixman is going to be better at conversion than we are.
Signed-off-by: NBenjamin Herrenschmidt <benh@kernel.crashing.org>

[ kraxel: just hook up qemu_pixman_check_format ]
Signed-off-by: NGerd Hoffmann <kraxel@redhat.com>

ui/vnc.c

@@ -2942,13 +2942,14 @@ static void vnc_listen_websocket_read(void *opaque)
 #endif /* CONFIG_VNC_WS */
 
 static const DisplayChangeListenerOps dcl_ops = {
-    .dpy_name          = "vnc",
-    .dpy_refresh       = vnc_refresh,
-    .dpy_gfx_copy      = vnc_dpy_copy,
-    .dpy_gfx_update    = vnc_dpy_update,
-    .dpy_gfx_switch    = vnc_dpy_switch,
-    .dpy_mouse_set     = vnc_mouse_set,
-    .dpy_cursor_define = vnc_dpy_cursor_define,
+    .dpy_name             = "vnc",
+    .dpy_refresh          = vnc_refresh,
+    .dpy_gfx_copy         = vnc_dpy_copy,
+    .dpy_gfx_update       = vnc_dpy_update,
+    .dpy_gfx_switch       = vnc_dpy_switch,
+    .dpy_gfx_check_format = qemu_pixman_check_format,
+    .dpy_mouse_set        = vnc_mouse_set,
+    .dpy_cursor_define    = vnc_dpy_cursor_define,
 };
 
 void vnc_display_init(DisplayState *ds)