Currently, there have no GMA500(Poulsbo) native video driver to support
intel opregion. So, use this stub driver to enable the acpi backlight
control sysfs entry files by requrest acpi_video_register.

[airlied: fix warnings]
Signed-off-by: NLee, Chun-Yi <jlee@novell.com>
Signed-off-by: NDave Airlie <airlied@redhat.com>