drm/nouveau: make flipping lockdep safe

cli->mutex was inverted with reservations, and multiple reservations were
used without a ticket, fix both. This commit had to be done after the previous
commit, because otherwise ttm_eu_* calls would use a different seqno counter..

Signed-off-by: Maarten Lankhorst <maarten.lankhorst@canonical.com>
Acked-by: Ben Skeggs <bskeggs@redhat.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>