drm/nouveau: Use drm_crtc_vblank_off/on

drm/nouveau: Use drm_crtc_vblank_off/on

With atomic nv50+ is already converted over to them, but the old
display code is still using it. Found in a 2 year old patch I have
lying around to un-export these old helpers!

v2: Drop the hand-rolled versions from resume/suspend code. Now that
crtc callbacks do this, we don't need a special case for s/r anymore.

v3: Remove unused variables.

v4: Don't remove drm_crtc_vblank_off from suspend paths, non-atomic
nouveau still needs that. But still switch to drm_crtc_vblank_off
since drm_vblank_off will disappear.

Cc: Mario Kleiner <[email protected]>
Cc: Ben Skeggs <[email protected]>
Reviewed-by: Alex Deucher <[email protected]>
Signed-off-by: Daniel Vetter <[email protected]>
Link: http://patchwork.freedesktop.org/patch/msgid/[email protected]