drm/nouveau: Use private save/restore hooks for CRTCs

I want to remove the core ones since with atomic drivers system
suspend/resume is solved much differently. And there's only 2 drivers
(gma500 besides nouveau) really using them.

v2: Fixup bugs Ilia spotted.

Cc: Ben Skeggs <bskeggs@redhat.com>
Cc: Ilia Mirkin <imirkin@alum.mit.edu>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/1449245618-1127-1-git-send-email-daniel.vetter@ffwll.ch


Reviewed-by: Thierry Reding <treding@nvidia.com>