Migrate to ecm_qt_declare_logging_category
Summary:
During D12656, it was suggested that it would be better to migrate to
ecm_qt_declare_logging_category.
Test Plan: It builds
Reviewers: Plasma, ivan, lbeltrame, davidedmundson
Reviewed By: Plasma, davidedmundson
Subscribers: plasma-devel
Tags: Plasma
Differential Revision: https://phabricator.kde.org/D12658