tty: serial: fsl_lpuart: enable two stop bits for lpuart32

Add two stop bits support.
User can run the command to enable two stop bits for test:
stty  cstopb  -F /dev/ttyLPx

Signed-off-by: Fugang Duan <fugang.duan@nxp.com>
Signed-off-by: Sherry Sun <sherry.sun@nxp.com>
Link: https://lore.kernel.org/r/20210823081733.31941-1-sherry.sun@nxp.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>