[platforms/drm] Add support for rotation property on the Plane

Summary:
A preparation step to support rotation of outputs. The idea is to rotate
using DRM directly and not add it to the compositors. With this change
and a small hack to try it, I was able to rotate the screen.

Reviewers: KWin, Plasma, subdiff

Subscribers: plasma-devel, kwin

Tags: KWin

Differential Revision: https://phabricator.kde.org/D8582