imx: mx6ul_14x14_evk: convert to DM_VIDEO

To support DM_VIDEO,
 Add display node for lcdif
 Drop board iomuxc settings.
 Enable DM_VIDEO

Signed-off-by: Peng Fan <peng.fan@nxp.com>
Reviewed-by: Anatolij Gustschin <agust@denx.de>