drm/i915/lvds: Always restore panel-fitter when enabling the LVDS

Linus Torvalds pointed out that our code was unbalanced when powering on
the panel with respect to the power off sequence in that we were failing
to restore the panel-fitter. The consequence of this would be that
across a simple DPMS off/on for a non-native mode, without an intervening
modeset, the panel fitter would remain disabled and the output would shift
on the panel.

Reported-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>