serial: imx: Remove unused platform data support

Since 5.10-rc1 i.MX is a devicetree-only platform and the existing
platform data support in this driver was only useful for old non-devicetree
platforms.

Get rid of the platform data support since it is no longer used.

Reviewed-by: Fugang Duan <fugang.duan@nxp.com>
Acked-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Fabio Estevam <festevam@gmail.com>
Link: https://lore.kernel.org/r/20201110214840.16768-1-festevam@gmail.com


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