i915: select VIDEO_OUTPUT_CONTROL for ACPI_VIDEO

fix Kconfig warning:

(DRM_I915 && STUB_POULSBO) selects ACPI_VIDEO which has unmet direct dependencies
(ACPI && X86 && BACKLIGHT_CLASS_DEVICE && VIDEO_OUTPUT_CONTROL && INPUT)

Signed-off-by: Konstantin Khlebnikov <khlebnikov@openvz.org>
Signed-off-by: Dave Airlie <airlied@redhat.com>