ACPI: video: output switch sysfs support

ACPI: video: output switch sysfs support

Requires CONFIG_VIDEO_OUTPUT_CONTROL and CONFIG_ACPI_VIDEO.

After loading output.ko and video.ko, you would have
/sys/class/video_output and several device acpi_videoNum there.

For example, I got acpi_video0, acpi_video1,acpi_video2,and acpi_video3
under /sys/class/video_output on my T40.
I can query the status of  output device0 by running " cat
/sys/class/video_output/acpi_video0
" The return value is defined in ACPI SPEC B.5.5 _DCS(Return the
Status of Output Device).  Also you can turn off video1 and turn on
video0  by " echo 0 > acpi_video1; echo 0x80000000 > acpi_video0".
Please reference ACPI SPEC  B.5.7 _DSS for the parameter definition.

Please note that it may or may NOT works purely depending on if
your vendor providing correct ACPI video extension support in bios.
the driver output.ko and video.ko just works like a interface to
invoke BIOS.

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