drm/i915/gt: Always try to reserve GGTT address 0x0

drm/i915/gt: Always try to reserve GGTT address 0x0

Since writing to address 0 is a very common mistake, let's try to avoid
putting anything sensitive there.

References: https://gitlab.freedesktop.org/drm/intel/-/issues/2989
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Matthew Auld <matthew.auld@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210125125033.23656-1-chris@chris-wilson.co.uk
Cc: stable@vger.kernel.org
(cherry picked from commit 56b429cc584c6ed8b895d8d8540959655db1ff73)
Signed-off-by: Jani Nikula <jani.nikula@intel.com>