linsysfs(5): Add support for recent libdrm

Expose more information about PCI devices (and GPUs in particular) via
linsysfs to libdrm.

This allows unmodified modern 64-bit Linux libdrm to work, which allows
modern Linux Mesa to work. The submitter reports that he tested the change
with an Ubuntu 16.04 chroot + amdgpu from graphics/drm-next-kmod.

PR: 222375
Submitted by: Greg V <greg AT unrelenting.technology>