media: cadence: csi2rx: Add get_fmt and set_fmt pad ops

The format is needed to calculate the link speed for the external DPHY
configuration. It is not right to query the format from the source
subdev. Add get_fmt and set_fmt pad operations so that the format can be
configured and correct bpp be selected.

Initialize and use the v4l2 subdev active state to keep track of the
active formats. Also propagate the new format from the sink pad to all
the source pads.

Signed-off-by: Pratyush Yadav <p.yadav@ti.com>
Tested-by: Julien Massot <julien.massot@collabora.com>
Reviewed-by: Maxime Ripard <mripard@kernel.org>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Tomi Valkeinen <tomi.valkeinen@ideasonboard.com>
Co-developed-by: Jai Luthra <j-luthra@ti.com>
Signed-off-by: Jai Luthra <j-luthra@ti.com>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>