drm/i915: Switch to drm_crtc variants of vblank functions

Where possible right now. Just a small step towards nirvana ...

v2: git add. Uggh. Noticed by Imre.

Cc: Imre Deak <imre.deak@intel.com>
Reviewed-by: Imre Deak <imre.deak@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>