Summary:
Control files are a relatively new concept and only used by the retention value
for now. Identify this data by the improved hash function, which also hashes
the name in case no EDID information is provided.

FIXED-IN: 5.17.3

Test Plan: Reads in and writes retention data.

Reviewers: #plasma, davidedmundson

Reviewed By: #plasma, davidedmundson

Subscribers: plasma-devel

Tags: #plasma

Differential Revision: https://phabricator.kde.org/D25021