Implment DRM EGL scaling
Summary: We need to set the viewport so that we scale from device pixels to global compositor space.
Test Plan:
Ran kwin_wayland properly on my laptop without setting KWIN_COMPOSE.
Most things worked.
Reviewers: Plasma
Subscribers: plasma-devel, kwin
Tags: KWin
Differential Revision: https://phabricator.kde.org/D3504