xf86drm: introduce drmGetDeviceNameFromFd2

The original version considered only card devices, while this will pick
the device/node name regardless - card, control, renderD, other...

Current implementation is "linux" specific, in such that it relies on
sysfs/uevent file. At the same time this gives us the flexibility to
support any nodes even future ones, as long as they're within DRM_MAJOR.

Shamelessly copied from mesa, latter by: Gary Wong <gtw@gnu.org>
Signed-off-by: Emil Velikov <emil.velikov@collabora.com>
Reviewed-by: Nicolai Hähnle <nicolai.haehnle@amd.com>