serial: imx: drop support for IRDA

Support for IRDA was added in 2009 in commit v2.6.31-rc1~399^2~2. There
are no in-tree users.

Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>