drm/i915: Re-apply "Perform link quality check, unconditionally during long pulse"

drm/i915: Re-apply "Perform link quality check, unconditionally during long pulse"

This re-applies the workaround for "some DP sinks, [which] are a
little nuts" from commit d4c73aa062ef ("drm/i915: Perform link
quality check unconditionally during long pulse").
It makes the secondary AOC E2460P monitor connected via DP to an
acer Veriton N4640G usable again.

This hunk was dropped in commit d08eea060c48 ("drm/i915: Move SST
DP link retraining into the ->post_hotplug() hook")

Fixes: d08eea060c48 ("drm/i915: Move SST DP link retraining into the ->post_hotplug() hook")
[Cleaned up commit message, added stable cc]
Signed-off-by: Lyude Paul <lyude@redhat.com>
Signed-off-by: Jan-Marek Glogowski <glogow@fbihome.de>
Cc: stable@vger.kernel.org
Link: https://patchwork.freedesktop.org/patch/msgid/20180825191035.3945-1-lyude@redhat.com