tools/libxl: Replace deprecated -sdl option on QEMU command line

"-sdl" is deprecated upstream since 6695e4c0fd9e ("softmmu/vl:
Deprecate the -sdl and -curses option"), QEMU v6.2, and the option is
removed by 707d93d4abc6 ("ui: Remove deprecated options "-sdl" and
"-curses""), in upcoming QEMU v7.1.

Instead, use "-display sdl", available since 1472a95bab1e ("Introduce
-display argument"), before QEMU v1.0.

Signed-off-by: Anthony PERARD <anthony.perard@citrix.com>
Reviewed-by: Jason Andryuk <jandryuk@gmail.com>

tools/libs/light/libxl_dm.c

@@ -1349,7 +1349,7 @@ static int libxl__build_device_model_args_new(libxl__gc *gc,
     flexarray_append_pair(dm_args, "-display", "none");
 
     if (sdl && !is_stubdom) {
-        flexarray_append(dm_args, "-sdl");
+        flexarray_append_pair(dm_args, "-display", "sdl");
         if (sdl->display)
             flexarray_append_pair(dm_envs, "DISPLAY", sdl->display);
         if (sdl->xauthority)