Add RS-485 support for SP0(J11) and SP4(J7)

The code opening the serial port needs to set the
termios after running an ioctl to put the driver in
485 mode.

struct serial_rs485 rs485conf;

/* Enable RS-485 mode: */
rs485conf.flags |= SER_RS485_ENABLED;

/* Set rts/txen delay before send, if needed: (in microseconds) */
rs485conf.delay_rts_before_send = 0;

/* Set rts/txen delay after send, if needed: (in microseconds) */
rs485conf.delay_rts_after_send = 0;

/* Write the current state of the RS-485 options with ioctl. */
if (ioctl (fd, TIOCSRS485, &rs485conf) < 0) {
        printf("Error: TIOCSRS485 ioctl not supported.\n");
}

Signed-off-by: Jeff Horn <jhorn@everlook.net>