Load QtQuickSettings for software rendering

We had support for falling back on errors yet somehow
the initial basic loading was missing.

Summary: BUG: 347772

Test Plan: Compiles

Reviewers: #plasma, broulik

Reviewed By: #plasma, broulik

Subscribers: plasma-devel

Tags: #plasma

Differential Revision: https://phabricator.kde.org/D14708