Revert "serial: imx-serial - move DMA buffer configuration to DT"

This reverts commit a3015aff as there
are complaints that it is incorrect.

Reported-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Cc: Nandor Han <nandor.han@ge.com>
Cc: Romain Perier <romain.perier@collabora.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>