uterm: drm: retry DRM wakeup after short timeout

If drm-wakeup fails, we now retry after 20ms continously to gain
DRM-Master again. If we succeed we send UTERM_REFRESH events for all
available displays so existing code can pick it up.

Signed-off-by: David Herrmann <dh.herrmann@gmail.com>
seat: forward UTERM_REFRESH events to sessions

On UTERM_REFRESH events we now forward the event to all sessions on the
bound seat. Sessions can then react to it and repaint the screen.

Signed-off-by: David Herrmann <dh.herrmann@gmail.com>
terminal: redraw on display-refresh

If we get a display-refresh event from the session layer, we must redraw
the screen to avoid staying blank.

Signed-off-by: David Herrmann <dh.herrmann@gmail.com>
dummy: redraw on display-refresh

If we get a display-refresh event, redraw the screen. Otherwise, we might
stay blank during VT switches if we get a delayed set-master.

Signed-off-by: David Herrmann <dh.herrmann@gmail.com>