Fix most systemsettings and kinfocenter KCM not being shown

For systemsettings we've been gradually moving around things in order to not rely on KServiceTypeTrader for loading KCMs in systemsettings

This caused those KCMs to be not found here using KServiceTypeTrader

To fix this take the loading logic from systemsettings and apply it here too

(cherry picked from commit 4b1a36ee)