drm/i915: don't set SDVO color range on ILK+

These bits are reserved on ILK+ (ILK+ provides this feature in the
transcoder and pipe configuration instead, which we already set).

Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Keith Packard <keithp@keithp.com>