drm/i915: Enable cmd parser to do secure batch promotion for aliasing ppgtt

With the binding regression from the original full ppgtt patches
fixed we can throw the switch. Yay!

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=90190


Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Reviewed-by: Mika Kuoppala <mika.kuoppala@intel.com>
[Jani: tweaked commit title per Chris' suggestion]
Signed-off-by: Jani Nikula <jani.nikula@intel.com>