drm: Save scaling and position of displays at shutdown

Summary:
Position and most importantly scaling will likely be the same on the next run,
This saves a flicker round at startup when scaling is different of 1 initialising the view at 1 then jumping at whatever the user requested.

Test Plan: Restarted my system several times

Reviewers: #kwin, #plasma, romangg

Reviewed By: #kwin, #plasma, romangg

Subscribers: davidedmundson, zzag, romangg, kwin

Tags: #kwin

Differential Revision: https://phabricator.kde.org/D22292