Make life easier by providing a function that hands
out the correct drm_vblank_crtc for a given a drm_crtc.

Also abstract the lower level internals of the vblank
code in a similar fashion.
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240408190611.24914-1-ville.syrjala@linux.intel.comReviewed-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>