systemd: Sync systemd-serialgetty@.service with upstream
The systemd upstream has been doing some improvements in the service
which were not in sync, with the forked file. Mainly:
- Use BindsTo to bind the service with the required serial device
- Add of getty-pre.target as dependency so we can run things before
getty@.service and serial-getty@.service
- Add conflicts to rescue to avoid issues with sulogin
We did not change the ExecStart and Environment fields so we don't have
side effects of this change.
Signed-off-by: Otavio Salvador <otavio@ossystems.com.br> Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
