media: imx: imx-mipi-csis: Set PIXEL_MODE for YUV422

Bits 13 and 12 of the ISP_CONFIGn register configure the PIXEL_MODE
which specifies the sampling size, in pixel component units, on the
CSI-2 output data interface when data are transferred to memory.

The register description in the chip manual specifies that DUAL mode
should be used for YUV422 data.

Signed-off-by: Jacopo Mondi <jacopo@jmondi.org>
Signed-off-by: Xavier Roumegue <xavier.roumegue@oss.nxp.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Acked-by: Rui Miguel Silva <rmfrfs@gmail.com>
Acked-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>