Revert "drm/i915: fix corruptions on i8xx due to relaxed fencing"

This reverts commit c2e0eb16.

As it turns out, userspace already depends upon being able to enable
tiling on existing bo which it promises to be large enough for its
purposes i.e. it will not access beyond the end of the last full-tile
row.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=35016


Reported-and-tested-by: Kamal Mostafa <kamal@canonical.com>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>