USB: serial: f81232: implement break control

Implement Fintek F81232 break on/off with LCR register.
It's the same with 16550A LCR register layout.

Signed-off-by: Ji-Ze Hong (Peter Hong) <hpeter+linux_kernel@gmail.com>
[ johan: fix corrupt line settings on break due to missing shadow_lcr
  update in set_termios() ]
Signed-off-by: Johan Hovold <johan@kernel.org>