The registers are the same as on Sandybridge.  Fixes scrambled display
in X when it does software drawing to the GTT, and scans the results
out as tiled.
Signed-off-by: NEric Anholt <eric@anholt.net>
Reviewed-by: NJesse Barnes <jbarnes@virtuousgeek.org>
Signed-off-by: NKeith Packard <keithp@keithp.com>