serial: imx: Remove unused members from imx_port struct

IRDA support is gone since commit afe9cbb1 ("serial: imx: drop
support for IRDA"), so remove the remaining irda members from
imx_port structure.

While at it, also remove 'trcv_delay' which is also unused.

Signed-off-by: Fabio Estevam <fabio.estevam@nxp.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>