media: imx: csi: enable double write reduction

For 4:2:0 subsampled YUV formats, avoid chroma overdraw by only writing
chroma for even lines. Reduces necessary write memory bandwidth by 25%.

Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>
Acked-by: Steve Longerbeam <steve_longerbeam@mentor.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>