media: ov2680: Add ov2680_mode struct

Add an ov2680_mode struct to group together mode related state.

For now this only contains the v4l2_mbus_framefmt and
the frame_interval.

This is a preparation patch for moving to calculating the per mode
settings, which will store more info in the new ov2680_mode struct.

Acked-by: Rui Miguel Silva <rmfrfs@gmail.com>
Reviewed-by: Daniel Scally <dan.scally@ideasonboard.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>