Switch from the driver-wide vblank vfuncs to the per-crtc ones so that
we don't have so many platform specific vfuncs in the driver struct.

We still need to do something about the rest fo the irq vfuncs...

v2: s/INTEL_GEN>=3/IS_GEN3/
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190619170842.20579-3-ville.syrjala@linux.intel.comReviewed-by: Chris Wilson <chris@chris-wilson.co.uk>