[platforms/drm] Restore previous mode if an atomic test fails

Summary:
When KWin successfully presents a new mode, it stores the current state
as the last working mode. If a new modeset is requested and the atomic
test fails, all is undone and reverted to this last knowing mode.

Currently included are:

• the mode
• global position
• transformation

This is only done on a modeset not when going to DPMS.

Test Plan:
Selected the not working vertical rotation and nothing bad
happened.

Reviewers: KWin, Plasma, subdiff

Subscribers: plasma-devel, kwin

Tags: KWin

Differential Revision: https://phabricator.kde.org/D8602