drm/i915: Be sure to turn hsync/vsync back on at crt enable (v2)

commit f40ebd6b
Author: Patrik Jakobsson <patrik.r.jakobsson@gmail.com>
Date:   Tue Mar 5 14:24:48 2013 +0100

    drm/i915: Turn off hsync and vsync on ADPA when disabling crt

properly disabled the hsync/vsync logic at disable time, but neglected
to re-enable them at enable time.

v2: In the enable hook, restore the connector's expected DPMS level
instead of forcing ON.  Do this by stashing a back pointer to the
connector in the crt (suggested by danvet) since otherwise it's awkward
to look up.

Signed-off-by: Adam Jackson <ajax@redhat.com>
Cc: stable@vger.kernel.org
[danvet: Added more verbose commit citation and cc: stable tag. Also,
make it compile. Then self-lart and try to assign the right pointer.]
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>