Revert "drm/i915: Add primary plane to mask if it's visible"

This reverts commit 721a09f7

.

There is nothing wrong with the commit per se. We had two versions of
the commit, one in -next headed for v4.4 and this one for v4.3. Turns
out we'll need to backport more fixes from -next, and they conflict with
the v4.3 version. It gets messy. It will be easiest to revert this one,
and backport all the relevant commits from -next without modifications;
they apply cleanly after this revert.

Requested-by: Joseph Yasi <joe.yasi@gmail.com>
References: https://bugs.freedesktop.org/show_bug.cgi?id=91910#c4
Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Acked-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>