drm/i915: Fix i965 secured batchbuffer usage

This 965G and above chipsets moved the batch buffer non-secure bits to
another place. This means that previous drm's allowed in-secure batchbuffers
to be submitted to the hardware from non-privileged users who are logged
into X and and have access to direct rendering.

Signed-off-by: Dave Airlie <airlied@redhat.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>