The i.MX driver defaulted to full duplex rs485 which is rather
unusual and doesn't match the default implemented in other drivers.

So change the default to half duplex.
Signed-off-by: NSascha Hauer <s.hauer@pengutronix.de>
Signed-off-by: NUwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>