media: staging: media: imx: imx7-media-csi: Add V4L2_PIX_FMT_Y14 support

The device supports 14-bit greyscale formats the same way it supports
14-bit Bayer formats.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Acked-by: Rui Miguel Silva <rmfrfs@gmail.com>
Tested-by: Alexander Stein <alexander.stein@ew.tq-group.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>