media: i2c: imx290: Add support for the mono sensor variant

Backport from https://patchwork.linuxtv.org/project/linux-media/list/?series=9918



The IMX290 module is available as either mono or colour (Bayer).

Update the driver so that it can advertise the correct mono
formats instead of the colour ones.

Signed-off-by: Dave Stevenson <dave.stevenson@raspberrypi.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Tested-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>