Map evdev keycode KEY_BRIGHTNESS_CYCLE to XF86MonBrightnessCycle

Add XF86MonBrightnessCycle keybinding, to be used as mapping for evdev's
KEY_BRIGHTNESS_CYCLE keycode which is generated from ACPI video module's
ACPI_VIDEO_NOTIFY_CYCLE_BRIGHTNESS on some Acer AIO desktop buttons.
The button changes the screen's brightness on Windows.

Fixes: https://bugs.freedesktop.org/show_bug.cgi?id=108861


Signed-off-by: Jian-Hong Pan <jian-hong@endlessm.com>