kcm_opengl: Fix retrieval of DRI information
Currently DRI information retrieval is attempted via /proc/dri, which
was removed from the linux kernel in v3.12 (2013). This information
includes the kernel driver in use as well as card identification sourced
from pci.ids database.
This adds support for retrieving this information in the same vein via
/dev and /sys for modern kernels.
Test Plan: kcmshell5 opengl should correctly display kernel driver.
Reviewers: Plasma, alexeymin
Reviewed By: alexeymin
Subscribers: alexeymin, wbauer, plasma-devel, Plasma
Differential Revision: https://phabricator.kde.org/D12476