The gd_egl_refresh function, as the name suggests, is responsible for
refreshing displays when using EGL graphics with QEMU's GTK UI. This is
a perfect candidate for a function to update the refresh rate in.

Since gd_monitor_update_interval is inaccessible from the gd_egl_refresh
function, we need to expose/globalize it in the include/ui/gtk.h file.

Signed-off-by: Nikola Pavlica <pavlica.nikola@gmail.com>
Message-Id: <20210114140153.301473-2-pavlica.nikola@gmail.com>
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>