drm-backend: really reset/restart outputs of a failed commit

This reverts f843ba34 ("drm-backend: limit
reset/restart to output of a failed commit") and actually solves the problem
correctly.

The pending_state is no longer valid at this point, so it cannot be used to
determine the outputs of the current commit. So only clear will_repaint when
starting to repaint, so it can be used to determine which outputs of a device
were actually repainted and use it to reset/restart those outputs.

Signed-off-by: Michael Olbrich <m.olbrich@pengutronix.de>