Register controls for V4L2_CID_HFLIP and V4L2_CID_VFLIP.

The controls are registered as read-only and enabled by default, as the
driver embeds a 180 degrees rotation in its programming sequences and
only supports that mode of operations.
Signed-off-by: Jacopo Mondi <jacopo.mondi@ideasonboard.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>