drm/nouveau: Display Nouveau boot options at launch

It can help to remove any ambiguity about which options were passed to Nouveau,
especially in case the user had some options set in /etc/modprobe.d/*.conf that
he forgot about, as they won't appear in a dmesg.

Signed-off-by: Pierre Moreau <pierre.morrow@free.fr>
Signed-off-by: Ben Skeggs <bskeggs@redhat.com>