Fixes these prints on boot:
[ 13.785600] imx-uart 2020000.serial: DMA transaction error.
[ 13.793134] imx-uart 2020000.serial: DMA transaction error.
[ 13.798721] imx-uart 2020000.serial: DMA transaction error.
Based on following upstream patch by Tim Harvey (Gateworks):
80a01b6582
TX complete DMA messages are getting missed.
This is also currently an issue in mainline.
For now we will disable DMA in serial/imx.c.
This resolves an issue encountered with RS485 transmit.
Signed-off-by: Koen Vandeputte <koen.vandeputte@ncentric.com>
