xf86drm: introduce drmGetDevice[s]2

Relative to the original version, here one can provide a flags bitmask.
Currently only DRM_DEVICE_IGNORE_PCI_REVISION is supported.

Implementation detail:
If it's set, we will only parse the separate sysfs files and we won't
touch the config one. The latter awakes the device (causing delays)
which is the core reason why this API was introduced.

v2:
 - Initialize revision to 0xff if it's unread.
 - Change DRM_DEVICE_IGNORE_PCI_REVISION to DRM_DEVICE_GET_PCI_REVISION
 - Add explicit note that drmGetDevice[s]2 does not retrieve the
revision by default.

v3:
 - Correctly fold drmParsePciDeviceInfo() hunk in this patch.

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>
Reviewed-by: Michel Dänzer <michel.daenzer@amd.com>