ACPI: thinkpad-acpi: make the video output feature optional

The video output port control feature is not very useful on many ThinkPads
(especially when a X server is running), and lately userspace is getting
better and better at it, so it makes sense to allow users to stripe out the
thinkpad-acpi video feature from their kernels and save at least 2KB.

Signed-off-by: Henrique de Moraes Holschuh <hmh@hmh.eng.br>
Signed-off-by: Len Brown <len.brown@intel.com>