drm/i915: don't save/restor ADPA for kms

We now no longer rely on this.

This is step 1 on a long journey to rid us of the save/restore
madness, which tends to lightly paper over many issues, and cause
tons of bad things itself ...

Reviewed-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
[danvet: satisfy Paulo's ocd and drop the needless braces.]
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>