drm/i915: Use i9xx_check_plane_surface() for sprite planes as well

drm/i915: Use i9xx_check_plane_surface() for sprite planes as well

All the pre-SKL sprite planes compute the x/y/tile offsets in a
similar way. There are a couple of minor differences but the primary
planes have those as well. Thus i9xx_check_plane_surface()
already does what we need, so let's use it.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20170323192712.30682-7-ville.syrjala@linux.intel.com
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>