graphics/intel-backlight: support newer GPUs and propose to take over maintainership on behalf of FreeBSDDesktop

[jmd]

Summary

The FreeBSDDesktop team proposes to maintain the intel-backlight port. This change includes a filed pull request from February 2017 (https://github.com/grembo/intel_backlight_fbsd/pull/3) which is necessary for working backlight control with newer GPUs as now supported through graphics/drm-next-kmod.

Test Plan

poudriere tested on amd64, i386 CURRENT, 10.3, 11.0 . Run tested by Johannes Lundberg and Pete Wright.

[grembo]

Thanks for taking over, I don't have any recent hardware or the time to maintain/test this myself at the moment.

[swills]

Approved, looks good