drm2 regression: backlight adjustment on ivybridge no longer works

[Miguel Clara]

On the laptop I'm running current, if relevant

Loading acpi_video doesn't do much....  I don't see any sysctl related to
"lcd0" or "birightness", this is one of those computers with "hybrid"
graphics, intel + ATI card, so not sure if that's somewhat related.


Anyway, I've just tested the drm patches (both) and intelbacklight (
https://github.com/grembo/intel_backlight_fbsd) compiles, installs and runs
fine!

So thanks both for the patches.