MLK-10886 CSI: Fix iMX6SL camera frame data split

i.MX6SL CSI IC have a limitation that DAM FIFO will auto start
when camera sensor power up.

In order to support camera sensor power up before CSI driver.
DMA FIFO should reset right before DMA FIFO enable,
otherwise FIFO will lost data and image will split.

Signed-off-by: Sandor Yu <R01008@freescale.com>