add opregion handling for drm2 - which exposes some ACPI video configuration
pieces that some Lenovo laptop models use to flesh out which video device
to speak to. This enables the brightness control in ACPI to work these models.
The CADL bits are also important - it's used to figure out which ACPI
events to hook the brightness buttons into. It doesn't yet seem to work
for me, but it does for the OP.
Tested:
* Lenovo X230 (mine)
* OP: ASUS UX51VZ
PR: 190186
Submitted by: Henry Hu <henry.hu.sh@gmail.com>
Reviewed by: dumbbell
works with new generations of GPUs (IronLake, SandyBridge and
supposedly IvyBridge).
The driver is not connected to the build yet.
Sponsored by: The FreeBSD Foundation
MFC after: 1 week
