drm/nouveau: replace legacy vblank helpers

Replace the legacy drm_send_vblank_event(), drm_arm_vblank_event() and
drm_vblank_{get,put}() with the new helper functions.

v2: add crtc to nouveau_page_flip_state (comment from Mario Kleiner)

Signed-off-by: Gustavo Padovan <gustavo.padovan@collabora.co.uk>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/1465308482-15104-1-git-send-email-gustavo@padovan.org