xf86drm: add plumbing to not retrieve PCI device revision

Will be used with the drmGetDevice[s]2 API.

Cc: Michel Dänzer <michel@daenzer.net>
Cc: Nicolai Hähnle <nhaehnle@gmail.com>
Cc: Mauro Santos <registo.mailling@gmail.com>
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=98502


Signed-off-by: Emil Velikov <emil.velikov@collabora.com>