drm/i915: Add scaled paramater to update_sprite_watermarks()

For calculating watermarks we want to know whether sprites are
scaled. Pass that information to update_sprite_watermarks() so that
eventually we may do some watermark pre-computing.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>