media: v4l2-ctrls: set AV1 sequence flags for testing

media: v4l2-ctrls: set AV1 sequence flags for testing

Initialize additional AV1 sequence parameters in std_init_compound()
to make the default AV1 sequence control compatible with compliance
and userspace testing tools.

Specifically, set:
 - enable both SUBSAMPLING_X and SUBSAMPLING_Y flags

These defaults help ensure that V4L2_CID_AV1_SEQUENCE behaves
consistently during validation and v4l2-compliance tests.

Signed-off-by: Pavan Bobba <opensource206@gmail.com>
Reviewed-by: Nicolas Dufresne <nicolas.dufresne@collabora.com>
[hverkuil: align everything a bit better]
[hverkuil: replaced Pavan's comment with comment suggested by Nicolas]
Signed-off-by: Hans Verkuil <hverkuil+cisco@kernel.org>