Sync scaling DPI from Plasma to SDDM
Summary: This patch adds scaling to the list of Plasma settings that can be synced with SDDM.
Displays->Scale Display->set to 1.5
Login Screen(SDDM)->Advanced->pressed "Sync"
SDDM was big.
Reviewers: Plasma, davidedmundson, ngraham
Reviewed By: Plasma, davidedmundson, ngraham
Differential Revision: https://phabricator.kde.org/D22700