Get rid of legacy DRM vblank function that are less clear to use.
The new ones basically requires only the crtc as parameters.

It also clean ups exynos_drm_crtc_finish_pageflip() parameters as a
consequence.
Signed-off-by: Gustavo Padovan <gustavo.padovan@collabora.co.uk>
Reviewed-by: Joonyoung Shim <jy0922.shim@samsung.com>
Signed-off-by: Inki Dae <inki.dae@samsung.com>