The explicit vblank handling was never finished. The driver never had
the full implementation of vblank and what was there is emulated
by DRM when the driver doesn't pretend to be implementing it itself.

Let DRM handle the vblank emulation and stop pretending the driver is
doing anything special with vblank. In the future it would make sense
to implement helpers for full vblank handling because vkms and
amdgpu_vkms already have that code. Exporting it to common helpers and
having all three drivers share it would make sense (that would be largely
just to allow more of igt to run).
Signed-off-by: Zack Rusin <zackr@vmware.com>
Reviewed-by: Maaz Mombasawala <mombasawalam@vmware.com>
Reviewed-by: Martin Krastev <krastevm@vmware.com>
Reviewed-by: Michael Banack <banackm@vmware.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20221022040236.616490-15-zack@kde.org