When using the frame packing and a single big framebuffer, some hardware
requires that we do everything like if we were scanning out the big
buffer itself. Let's instrument drm_mode_set_crtcinfo() to be able to do
this adjustement if the driver is asking for it.

v2: Use crtc_vtotal and multiply the clock by 2 instead of
    reconstructing it (Ville Syrjälä)
Suggested-by: NDaniel Vetter <daniel.vetter@ffwll.ch>
Reviewed-by: NVille Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: NDamien Lespiau <damien.lespiau@intel.com>
Acked-by: NDave Airlie <airlied@gmail.com>
Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>