Implement back-light control for internal displays.
If system has 1 internal display and
/sys/class/backlight/backlight/brightness,
/sys/class/backlight/backlight/max_brightness
is availabe / accessible, HAL API can be redirected to this sysfs entries.
This could be extended in the future using external configuration to map display to brightness controller.
weston reference: https://gitlab.freedesktop.org/wayland/weston/-/blob/master/libweston/backend-drm/libbacklight.c