tty: serial: lpuart: Add RS485 support for 32-bit uart flavour

This commits adds RS485 support for LPUART hardware that uses 32-bit
registers. These are typically found in i.MX8 processors.

Signed-off-by: Philippe Schenker <philippe.schenker@toradex.com>
Reviewed-by: Fugang Duan <fugang.duan@nxp.com>

Link: https://lore.kernel.org/r/20191017141428.10330-3-philippe.schenker@toradex.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>