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.
Making it optional also makes it much easier to deprecate and remove the
feature eventually.
Signed-off-by: Henrique de Moraes Holschuh <hmh@hmh.eng.br>