imx6: disable UART dma

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: Tim Harvey <tharvey@gateworks.com>

target/linux/imx6/patches-4.4/306-disable-uart-dma.patch

@@ -0,0 +1,14 @@
+--- a/drivers/tty/serial/imx.c
++++ b/drivers/tty/serial/imx.c
+@@ -1146,9 +1146,11 @@ static int imx_startup(struct uart_port
+ 	writel(temp & ~UCR4_DREN, sport->port.membase + UCR4);
+
+ 	/* Can we enable the DMA support? */
++/*
+ 	if (is_imx6q_uart(sport) && !uart_console(port) &&
+ 	    !sport->dma_is_inited)
+ 		imx_uart_dma_init(sport);
++*/
+
+ 	spin_lock_irqsave(&sport->port.lock, flags);
+ 	/* Reset fifo's and state machines */