drm/i915: apply timing generator bug workaround on CPT and PPT

drm/i915: apply timing generator bug workaround on CPT and PPT

commit 3bcf603f6d5d18bd9d076dc280de71f48add4101 upstream.

On CougarPoint and PantherPoint PCH chips, the timing generator may fail
to start after DP training completes.  This is due to a bug in the
FDI autotraining detect logic (which will stall the timing generator and
re-enable it once training completes), so disable it to avoid silent DP
mode setting failures.

Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>
Signed-off-by: Keith Packard <keithp@keithp.com>
Signed-off-by: Timo Aaltonen <timo.aaltonen@canonical.com>