drm/i915: Unify ivb_update_cursor() and i9xx_update_cursor()

Ever since
 commit 5efb3e28
 Author: Ville Syrjälä <ville.syrjala@linux.intel.com>
 Date:   Wed Apr 9 13:28:53 2014 +0300

    drm/i915/chv: Add cursor pipe offsets

the only difference between i9xx_update_cursor() and ivb_update_cursor()
was the hsw+ pipe csc handling. Let's unify them and we can rid
outselves of some duplicated code.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>