TTY: simserial, use tty_port_open

So now we convert startup to be ->activate of tty_port. This means we
no longer care about INITIALIZED and TTY_IO_ERROR flags.

After we have ->activate much of the code may go as it duplicates what
tty_port_open does. In this case tty_port_open adds block_til_ready to
the path. But we do not define carrier hooks, so it is a noop.

Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Cc: Tony Luck <tony.luck@intel.com>
Cc: Fenghua Yu <fenghua.yu@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>