drm/radeon/dce6: add missing display reg for tiling setup

commit 7c1c7c18 upstream.

A new tiling config register for the display blocks was
added on DCE6.

May fix:
https://bugs.freedesktop.org/show_bug.cgi?id=62889
https://bugs.freedesktop.org/show_bug.cgi?id=57919



Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>