thinkpad-acpi: lock down video output control to root only
Jidani reports that, given the right combination of ThinkPad and
X.org, just reading the video output control state can crash X.org.
Until the day I somehow find out a model or BIOS cut date to not
provide this feature to ThinkPads that can do video switching through
X RandR, change permissions so that only processes with CAP_SYS_ADMIN
can access any sort of video output control state.
Reported-by: Jidani
Signed-off-by: Henrique de Moraes Holschuh <hmh@hmh.eng.br>