drm/i915: fix PCH eDP SSC support

Enable SSC on PCH eDP if possible.

Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>
[ickle: added a posting read of PCH_DREF_CONTROL before the udelay]
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
1 file changed