imx6: fix DMA transaction errors

Following errors were seen in the past on imx6 when using serial:

[ 22.617622] imx-uart 2020000.serial: DMA transaction error.
[ 22.623228] imx-uart 2020000.serial: DMA transaction error.
[ 22.628826] imx-uart 2020000.serial: DMA transaction error.
[ 22.648951] imx-uart 2020000.serial: DMA transaction error.
[ 22.654558] imx-uart 2020000.serial: DMA transaction error.
[ 22.660156] imx-uart 2020000.serial: DMA transaction error.

Which is the reason why DMA for the serial ports
got disabled in commits:

efb362cd93 ("imx6: disable dma on uart")
3b4241071d ("imx6: disable UART dma")

As indicated on mailinglist discussion, the cause seems to be
the usage of very old SDMA firmware which is present in the soc:

[    0.624302] imx-sdma 20ec000.sdma: Direct firmware load for imx/sdma/sdma-imx6q.bin failed with error -2
[    0.624318] imx-sdma 20ec000.sdma: Falling back to user helper
[   64.531607] imx-sdma 20ec000.sdma: external firmware not found, using ROM firmware

This patch adds the new firmware binary. (2196 bytes)

It is required to embed the binary into the kernel image, as it
gets loaded very early in the boot process where the rootfs is not
available yet:

[    0.622966] imx-sdma 20ec000.sdma: loaded firmware 3.3

Extended testing shows that the DMA errors are not seen anymore
when using this newer firmware version.

Signed-off-by: Koen Vandeputte <koen.vandeputte@ncentric.com>

target/linux/imx6/config-4.14

@@ -185,6 +185,8 @@ CONFIG_F2FS_FS=y
 # CONFIG_F2FS_FS_SECURITY is not set
 CONFIG_F2FS_FS_XATTR=y
 CONFIG_F2FS_STAT_FS=y
+CONFIG_EXTRA_FIRMWARE="imx/sdma/sdma-imx6q.bin"
+CONFIG_EXTRA_FIRMWARE_DIR="firmware"
 CONFIG_FEC=y
 CONFIG_FIXED_PHY=y
 CONFIG_FIX_EARLYCON_MEM=y

target/linux/imx6/patches-4.14/210-disable-uart-dma.patch

@@ -1,23 +0,0 @@
-Based on following upstream patch by Tim Harvey (Gateworks):
-
-https://github.com/Gateworks/openwrt/commit/80a01b6582f94c4547f39d3a25e0a1e9b6eb9877
-
-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.
-
---- a/drivers/tty/serial/imx.c
-+++ b/drivers/tty/serial/imx.c
-@@ -1268,10 +1268,6 @@ static int imx_startup(struct uart_port
- 
- 	writel(temp & ~UCR4_DREN, sport->port.membase + UCR4);
- 
--	/* Can we enable the DMA support? */
--	if (!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 */
- 	i = 100;