drm/i915: Update plane parameters for cursor plane (v2)

This allows the cursor plane to be updated the same way as primary and sprites,
and same set_property handler is used for all of these planes.

v2 (by Matt Roper): Rework to apply to latest di-nightly codebase.  The
        switch to split check/commit plane programming changed the code
        flow enough that the original patch could no longer be applied.

Signed-off-by: Sonika Jindal <sonika.jindal@intel.com>
Reviewed-by: Matt Roper <matthew.d.roper@intel.com>
Tested-by (IVB): Matt Roper <matthew.d.roper@intel.com>
Signed-off-by: Matt Roper <matthew.d.roper@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>