ACPI: video: fix build for VIDEO_OUTPUT_CONTROL=n

drivers/built-in.o: In function `acpi_video_bus_put_devices':
video.c:(.text+0x79663): undefined reference to
`video_output_unregister'
drivers/built-in.o: In function `acpi_video_bus_add':
video.c:(.text+0x7b0b3): undefined reference to `video_output_register'

Signed-off-by: Len Brown <len.brown@intel.com>