drm/nouveau: Handle frame-packing mode geometry and timing effects

Frame-packing modes add an extra vtotal raster lines to each frame
above and beyond what the basic mode description calls for.
Account for this during scaler configuration (possibly a bit of a
hack), during CRTC configuration (clearly not a hack), and when
checking that a mode is valid for a given connector (cribbed from
the i915 driver).

Signed-off-by: Alastair Bridgewater <alastair.bridgewater@gmail.com>
Signed-off-by: Ben Skeggs <bskeggs@redhat.com>