Debug output for platforms
Summary: Mostly so DRM can report if it has AMS or not
Test Plan:
Ran on my DRM setup, printed debug.
Spawned nested compositor, printed debug on that
Reviewers: Plasma, graesslin
Reviewed By: Plasma, graesslin
Subscribers: plasma-devel, kwin, KWin
Tags: KWin
Differential Revision: https://phabricator.kde.org/D8702