drm/i915: Move unload time opregion unregistration earlier

Move the opregion unregistration earlier to match its corresponding
registration order.

Signed-off-by: Imre Deak <imre.deak@intel.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: http://patchwork.freedesktop.org/patch/msgid/1458128348-15730-14-git-send-email-imre.deak@intel.com