drm/i915/guc: Revert "drm/i915/guc: enable GuC loading & submission by default"

This reverts commit 041824ee.

We have latency issues that might impact the performance: #96606.
and hangs and loading issues on resume after S4: #96526.

This is also blocking a platform milestone so let's disable
this for now while we make sure we don't have any more loading
issue, or related basic hangs and it pass BAT for real in all
platofmrs.

In case BAT is wrong let's first fix BAT before re-enable it here.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=96606
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=96526


Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Dave Gordon <david.s.gordon@intel.com>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Cc: Stable <stable@vger.kernel.org>
Cc: Jani Nikula <jani.nikula@intel.com>
Cc: Christophe Prigent <christophe.prigent@intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/1468884477-30086-1-git-send-email-rodrigo.vivi@intel.com