imx: convert mx6cuboxi board to DM_VIDEO

Migration to DM_VIDEO driver is long overdue. Update defconfig
to enable usage of converted ipuv3 driver DM configuration.

Signed-off-by: Anatolij Gustschin <agust@denx.de>
Cc: Baruch Siach <baruch@tkos.co.il>
Cc: Fabio Estevam <fabio.estevam@nxp.com>